I just tried Sublime 2 and I must admit I don't "get it." It seems like a basic editor with several features which Notepad++ already had. Specifically for programming I cannot see why you would use this as opposed to something like Visual Studio with its context aware auto-complete (massive productivity increase). But then again I also don't get why someone would use Vim or Emacs when you have GUI based tools availab…
IDEs are valuable when doing what they were designed for (I use Eclipse when I write Android apps, and I'd probably use Visual Studio if I was going to write something for the MS stack), but I'm rarely doing things that fit nicely into their world, and I end up spending more time fighting with them than they are worth.
That's just for me though.
Also: you can get completion in many text editors if you install the right plugins. See the GoSublime extension that I mentioned for example.