I'd probably take the opportunity to not mess things up as badly as I did the first time around. The past two years have been a string of catastrophic failures with members of the opposite sex (each of which has been the result of mistakes made glaringly obvious in hindsight), so it'd be nice to be able to go through that sequence again and maybe make one or two things work out.
Other than that, though, it would kind of suck. Two years ago, I was a little bit fucked up and creeped most people out. I've cleared my head a bit, stopped trying too hard, and get on better with people, so it would kind of suck to be dropped back into a low point in my life. Also, it would just be DULL most of the time. It's all stuff that I've done before, already learned, etc., so going back through it all again would be mind-numbing. That said, I do regret not setting aside more time to learn things (those two years might be great for starting to teach myself to code earlier), so at least there's that.
Basically, it would be an odd mix of boring, troubling, and frustrating to be dropped back into my life circa 2009, but it'd be nice to have a second chance at everything I've done since then.