I've been using TextMate for years and I'm productive and happy with it. However, I like to try other editors from time to time to see if I'm missing anything. Recently I spent some time learning Vim and I discovered a few things that I particularly liked.
1) Split windows -- not the kind of split windows you normally get in Mac applications, but the Vim style ones. In Vim you can easily navigate from the keyboard to your different splits and choose what files to display in each. Additionally, you don't have to reach for your mouse to create a split. When you split, Vim divides the space up for you which is what you want most of the time. I found that it is very handy when needing to view more than 1 file at a time, which in my case is most of the time. Closing splits is about as easy as they are to create -- all from the keyboard. Multiple windows isn't really the same thing because they are slow to setup and tear down.
2) Selective multifile grep -- in Vim you can use a regular expression to open a set of files, and then just grep across the open files.
3) Don't need arrow keys -- after years of editing with the mouse; I find it painful to reach for it. It hurts my right shoulder and shoulder blade. It even hurts to have to move my hand down to the arrow keys. However, in Vim it is easy to keep your hands resting on your keyboard with your shoulders relaxed. No reaching for the mouse or arrow keys.