Something I've seen over the last six months to a year (it may be older): using "this" as a one word reply agreeing to a previous comment in a thread. E.g. "It's not that C++ is a complex language, it's simply that programmers tend to fail more spectacularly when using it." Followed by: "This." (Often with an up arrow ^ reemphasizing the direction of the this). Maybe an abbrev. of "this is what I mean" or "this is what I'm talking about" or perhaps just "this is the real issue." It usually follows a very long post and so makes an exaggerated point in its brevity of how well the previous post has encapsulated the heart of the discussion.
[ updated 23 Dec 2009 ]
Over the past couple of months, there's been a backlash of anti-brevity. Here's one humorous example of this-hatred: