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 => 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?