Here is the output after a MAcPorts uninstall ():

$ sudo port install mongodb
--->  Computing dependencies for mongodb
--->  Dependencies to be installed: libpcap pcre bzip2 libedit ncurses zlib scons python27 db46 gettext expat libiconv openssl python_select sqlite3 snappy lzo2 spidermonkey nspr
--->  Fetching archive for libpcap
--->  Attempting to fetch libpcap-1.3.0_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/libpcap
--->  Attempting to fetch libpcap-1.3.0_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/libpcap
--->  Installing libpcap @1.3.0_0
--->  Activating libpcap @1.3.0_0
--->  Cleaning libpcap
--->  Fetching archive for bzip2
--->  Attempting to fetch bzip2-1.0.6_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/bzip2
--->  Attempting to fetch bzip2-1.0.6_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/bzip2
--->  Installing bzip2 @1.0.6_0
--->  Activating bzip2 @1.0.6_0
--->  Cleaning bzip2
--->  Fetching archive for ncurses
--->  Attempting to fetch ncurses-5.9_1.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/ncurses
--->  Attempting to fetch ncurses-5.9_1.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/ncurses
--->  Installing ncurses @5.9_1
--->  Activating ncurses @5.9_1
--->  Cleaning ncurses
--->  Fetching archive for libedit
--->  Attempting to fetch libedit-20120601-3.0_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/libedit
--->  Attempting to fetch libedit-20120601-3.0_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/libedit
--->  Installing libedit @20120601-3.0_0
--->  Activating libedit @20120601-3.0_0
--->  Cleaning libedit
--->  Fetching archive for zlib
--->  Attempting to fetch zlib-1.2.7_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/zlib
--->  Attempting to fetch zlib-1.2.7_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/zlib
--->  Installing zlib @1.2.7_0
--->  Activating zlib @1.2.7_0
--->  Cleaning zlib
--->  Fetching archive for pcre
--->  Attempting to fetch pcre-8.31_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/pcre
--->  Attempting to fetch pcre-8.31_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/pcre
--->  Installing pcre @8.31_0
--->  Activating pcre @8.31_0
--->  Cleaning pcre
--->  Fetching archive for db46
--->  Attempting to fetch db46-4.6.21_7.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/db46
--->  Attempting to fetch db46-4.6.21_7.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/db46
--->  Installing db46 @4.6.21_7
--->  Activating db46 @4.6.21_7
--->  Cleaning db46
--->  Fetching archive for expat
--->  Attempting to fetch expat-2.1.0_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/expat
--->  Attempting to fetch expat-2.1.0_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/expat
--->  Installing expat @2.1.0_0
--->  Activating expat @2.1.0_0
--->  Cleaning expat
--->  Fetching archive for libiconv
--->  Attempting to fetch libiconv-1.14_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/libiconv
--->  Attempting to fetch libiconv-1.14_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/libiconv
--->  Installing libiconv @1.14_0
--->  Activating libiconv @1.14_0
--->  Cleaning libiconv
--->  Fetching archive for gettext
--->  Attempting to fetch gettext-0.18.1.1_2.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/gettext
--->  Attempting to fetch gettext-0.18.1.1_2.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/gettext
--->  Installing gettext @0.18.1.1_2
--->  Activating gettext @0.18.1.1_2
--->  Cleaning gettext
--->  Fetching archive for openssl
--->  Attempting to fetch openssl-1.0.1c_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/openssl
--->  Attempting to fetch openssl-1.0.1c_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/openssl
--->  Installing openssl @1.0.1c_0
--->  Activating openssl @1.0.1c_0
--->  Cleaning openssl
--->  Fetching archive for python_select
--->  Attempting to fetch python_select-0.3_1.darwin_11.noarch.tbz2 from http://lil.fr.packages.macports.org/python_select
--->  Attempting to fetch python_select-0.3_1.darwin_11.noarch.tbz2.rmd160 from http://lil.fr.packages.macports.org/python_select
--->  Installing python_select @0.3_1
--->  Activating python_select @0.3_1
--->  Cleaning python_select
--->  Fetching archive for sqlite3
--->  Attempting to fetch sqlite3-3.7.14.1_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/sqlite3
--->  Attempting to fetch sqlite3-3.7.14.1_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/sqlite3
--->  Installing sqlite3 @3.7.14.1_0
--->  Activating sqlite3 @3.7.14.1_0
--->  Cleaning sqlite3
--->  Fetching archive for python27
--->  Attempting to fetch python27-2.7.3_1.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/python27
--->  Attempting to fetch python27-2.7.3_1.darwin_11.x86_64.tbz2 from http://mse.uk.packages.macports.org/sites/packages.macports.org/python27
--->  Attempting to fetch python27-2.7.3_1.darwin_11.x86_64.tbz2.rmd160 from http://mse.uk.packages.macports.org/sites/packages.macports.org/python27
--->  Installing python27 @2.7.3_1
--->  Activating python27 @2.7.3_1

To make python 2.7 the default (i.e. the version you get when you run 'python'), please run:

sudo port select --set python python27

--->  Cleaning python27
--->  Fetching archive for scons
--->  Attempting to fetch scons-2.2.0_0.darwin_11.noarch.tbz2 from http://lil.fr.packages.macports.org/scons
--->  Attempting to fetch scons-2.2.0_0.darwin_11.noarch.tbz2.rmd160 from http://lil.fr.packages.macports.org/scons
--->  Installing scons @2.2.0_0
--->  Activating scons @2.2.0_0
--->  Cleaning scons
--->  Fetching archive for lzo2
--->  Attempting to fetch lzo2-2.05_1.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/lzo2
--->  Attempting to fetch lzo2-2.05_1.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/lzo2
--->  Installing lzo2 @2.05_1
--->  Activating lzo2 @2.05_1
--->  Cleaning lzo2
--->  Fetching archive for snappy
--->  Attempting to fetch snappy-1.0.5_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/snappy
--->  Attempting to fetch snappy-1.0.5_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/snappy
--->  Installing snappy @1.0.5_0
--->  Activating snappy @1.0.5_0
--->  Cleaning snappy
--->  Fetching archive for nspr
--->  Attempting to fetch nspr-4.8.9_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/nspr
--->  Attempting to fetch nspr-4.8.9_0.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/nspr
--->  Installing nspr @4.8.9_0
--->  Activating nspr @4.8.9_0
--->  Cleaning nspr
--->  Fetching archive for spidermonkey
--->  Attempting to fetch spidermonkey-1.7.0_5.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/spidermonkey
--->  Attempting to fetch spidermonkey-1.7.0_5.darwin_11.x86_64.tbz2.rmd160 from http://lil.fr.packages.macports.org/spidermonkey
--->  Installing spidermonkey @1.7.0_5
--->  Activating spidermonkey @1.7.0_5
--->  Cleaning spidermonkey
--->  Fetching archive for mongodb
--->  Attempting to fetch mongodb-2.2.1_0.darwin_11.x86_64.tbz2 from http://lil.fr.packages.macports.org/mongodb
--->  Attempting to fetch mongodb-2.2.1_0.darwin_11.x86_64.tbz2 from http://mse.uk.packages.macports.org/sites/packages.macports.org/mongodb
--->  Attempting to fetch mongodb-2.2.1_0.darwin_11.x86_64.tbz2 from http://packages.macports.org/mongodb
--->  Fetching distfiles for mongodb
--->  Attempting to fetch mongodb-src-r2.2.1.tar.gz from http://lil.fr.distfiles.macports.org/mongodb
--->  Verifying checksum(s) for mongodb
--->  Extracting mongodb
--->  Applying patches to mongodb
--->  Configuring mongodb
--->  Building mongodb
Error: org.macports.build for port mongodb returned: command execution failed
Please see the log file for port mongodb for details:
    /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_databases_mongodb/mongodb/main.log
To report a bug, follow the instructions in the guide:
    http://guide.macports.org/#project.tickets
Error: Processing of port mongodb failed