Rubymine has a fairly decent VIM mode ( http://plugins.intellij.net/plugin/?id=164 ) but its a lot less snappy than MacVim.

I only use it (Rubymine) now and again though, for things like browsing through projects I don't work on often, or to help find syntax errors in code and so on.

Could it be that you use debugger so rarely because its so difficult and not user-friendly in command line mode? I run my application in debug mode all the time so that i can stop it at any time and look at different values and states at all possible levels of execution stack

Maybe. I find that if the code I'm working with is decently written (i.e. paired on, done via decent TDD or BDD), then the need for a debugger rarely arises.

I'm a vim user. I'd use RM when pairing with someone not well versed in vim. Otherwise, I find it slow and difficult to work in.