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Oh, another thing about this feature, as implemented in SlickEdit. In the older versions of SlickEdit, completion features were "on demand", i.e. triggered by the programmer pressing a key. Thus the programmer usually knows what he's trying to do, presses the correct key, and gets what he wants.
Later versions of SlickEdit (last 10 years or so) moved to a more "automatic" mode. The editor tries to second-guess the programmer, and usually gets it wrong. Thus with current-day SlickEdit I often end up with text in my buffer that is different from what I typed -- very annoying. 
I prefer an editor that lets me decide what to complete rather than trying to outguess me. And I find it very frustrating if I type something and the editor enters something else.
Please consider this feature. It's simple, but deceptively powerful, and can be used in a wide variety of tasks.
I've been relying on it since I first discovered SlickEdit in 1996, and would really love to see this in Sublime Text 2.
John Hurst