Excerpted from The State of the Web – Summer 2008, a clever commentary in illustration form by web designer Matthew Inman:
If you don’t get all of the web-geeky references in the picture, you’re not alone (anyone want to fill me in on what the “Rick/Never gonna give you up, etc.” thing is?). I’ll own up to my penchant for Facebook, but I have been cutting way back on the SuperPoking.
If this is your first visit to C&B you may be wondering, "Who the hell is this guy, and why does he have a blog?" It's a fair question, so I've dedicated an entire page to answering it: check out 
Your answer = http://en.wikipedia.org/wiki/Rickroll
My question = what’s the two girls and a cup thing about??
Believe me, you don’t want to know. OK, I realize that by saying that I’ve made it so you do want to know even more than before… well, don’t say I didn’t warn you.
The wikipedia answer to your question is here. Whatever you do, I strongly encourage you to NOT watch the original video. I haven’t, and I plan on keeping it that way.
That said, I did get a pretty big kick out of this “reaction” video.