I recently switched to vim7 and discovered this lovely thing called Omnicompletion. Combined with stuff like vimtags it can deliver an experience very similar to big IDEs, with a nice menu popping up and displaying a list of available functions for that object.
The other big improvement is 256 colors support and a new theme taking advantage of it. It sounds like eye-candy but it's a pure functional enhancement, making me able to read code a lot faster than I used to be when lots of stuff looked like the same. And smoother colors are also nicer to the eyes for long coding sessions. Tabs are much nicer than buffers and the minibuffer plugin, and an enhanced status line can save you quite a few keystrokes and provide some very useful information more »