>>48-51
I think the terms are a bit nebulous and depend on who you ask. Some people think HTML webpages with cgi-bin scripts are the beginning of web 2.0, and those sites date back to the late 90s. I think for most people though, web 2.0 is a design philosophy. The era of round corners, gradients, icons, user interaction, and so on. Social media is probably the biggest delineating point, but then again, blogs and forums and 2ch style BBSes fall into that category as well.

It's just one of those things that you know when you see it. The details are a bit murky though.