Mongrel Hangs

When I run script/server, Mongrel hangs. If I ctrl-c, it does this...

Gavin$ script/server
^C=> Booting Mongrel (use 'script/server webrick' to force WEBrick)
=> Rails application starting on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server

...and then hangs again. What's going on? I've removed and
reinstalled Mongrel with no effect. This all started when I did 'gem
cleanup'. Perhaps I removed some dependency? How do I get this
working again?