Longer version: For anyone who hasn't, it's short for Let's Meet In Real Life. I've seen it twice now--both times offline. The most appropriate response I could formulate was OMGWTFBBQ... because who DOES that? I've met 'Net friends IRL myself, and it has NEVER been that casual unless they're the friend of a friend I already know. Even then, we've never used that or anything like it.
Of course, when I saw that headline today, it also mentioned kids texting it to each other. Yes, by cell phone. If you already have someone's number and you're going to suggest a meeting, I'd think you'd do it during an actual call...
Then again, this is probably the same type of people who thought "yeah, I'd hit that" was a good ad campaign slogan for both a McDonald's hamburger and the PSP. >_>
[x-posted for more angry letter fodder]