Vim bindings are nice, but when I have to use an IDE, the one feature I want is the ability to make files open up in Vim for editing.

I'm OK with having an IDE window hiding behind my Vim window, to switch to for when I need to click on a Build button, or a built-in debugger to use on occasion. I just absolutely want to have my files open up in Vim when it's time to manipulate text.

This used to be possible in Xcode and it was taken away with Xcode 4. (I'm unaware of any workaround, though I will go hunting for one next time I am on an iOS project)