I couldn't imagine using standalone vim as an IDE either... However, if you want the best of both worlds then Visual Studio has a vim emulation plugin (VsVim) and Sublime has vim emulation mode too!
Yep, it is the vim bindings and mode based editing that I love. XVim for Xcode, IdeaVim for Idea, and all those editors with vim modes. I used to hate vim, but once I got used to it, I'm just so much faster.
It depends, but if you do Haskell, with syntastic and ghcmod-vim, you get most of what I care about in an IDE, namely getting warning of errors before trying to run my program.
The Vim plugin for Visual Studio is very good, in my memory. Note that Kate has also a pretty good Vim mode. There is also a decent free Vim plugin for Eclipse [1].