Vim is an extremely mature editor with a well-established feature set. MacVim provides a nice native Cocoa interface to that solid core, and is pretty robust itself. So since I started using it full-time at the start of this year I've never felt the need to run anything but the latest stable release.
I wanted to drag proxy icons from the window titlebar to my file transfer client in order to initiate some uploads, and guess what? You can't drag them in the latest stable release, but in the latest snapshot (currently "snapshot 45") you can. So time to update!