When starting the daemon - there is no indication that the daemon fails to start except of course that you can't connect.

[11:00][andy@andy:~]$ sudo /etc/rc.d/mongodb start
:: Starting mongodb [DONE]
[11:00][andy@andy:~]$ mongo
MongoDB shell version: 1.6.2
connecting to: test
Tue Nov 30 11:00:28 Error: couldn't connect to server 127.0.0.1} (anon):1137
exception: connect failed
[11:00][andy@andy:~]$ more /var/log/mongod
Tue Nov 30 11:00:23 MongoDB starting : pid=4319 port=27017 dbpath=/var/state/mongodb 64-bit
Tue Nov 30 11:00:23 db version v1.6.2, pdfile version 4.5
Tue Nov 30 11:00:23 git version: nogitversion
Tue Nov 30 11:00:23 sys info: Linux andy 2.6.34-ARCH #1 SMP PREEMPT Mon Jul 5 22:12:11 CEST 2010 x86_64 BOOST_LIB_VERSION=1_43

• • • • • • • • • • • • • • old lock file: /var/state/mongodb/mongod.lock. probably means unclean shutdown
                            recommend removing file and running --repair
                            see: http://dochub.mongodb.org/core/repair for more information
                            *************
                            Tue Nov 30 11:00:23 exception in initAndListen std::exception: old lock file, terminating
                            Tue Nov 30 11:00:23 dbexit:

Tue Nov 30 11:00:23 shutdown: going to close listening sockets...
Tue Nov 30 11:00:23 shutdown: going to flush oplog...
Tue Nov 30 11:00:23 shutdown: going to close sockets...
Tue Nov 30 11:00:23 shutdown: waiting for fs preallocator...
Tue Nov 30 11:00:23 shutdown: closing all files...
Tue Nov 30 11:00:23 closeAllFiles() finished

Tue Nov 30 11:00:23 dbexit: really exiting now

Obviously, if you're starting things manually you can immediately check the log to see the reason (in this case, a power cut). but it'd be a lot simpler to identify that something isn't right if the deamon script returned [FAIL] if it couldn't start.

I'm not sure if the rc.d script falls directly under the main project - therefore apologies in advance if this is the wrong bug tracker to use.