There's been a lot of talk about "Web 2.0" - what is it, and why should you care?
It's Internet-based collaboration, via new tools, technologies and websites. At one end of the scale, it's been adopted by teens (e.g. myspace.com) - similar to their rapid adoption of mobile phone technologies. At the other end, it's web-based business collaboration: both within an organisation, and between businesses.
So you don't fit into those marketplaces right now, so why should you care? Because it signals an interactive approach to the internet - not humans interacting with computers, but humans with humans - computers are just tools (as they should be!). And it will become pervasive. You will catch up with it, or it will catch up with you. So far, it's largely with early adoptors - like teens and tech companies.
For lots of examples of Web 2.0 applications, try Web2.0Slides. Meanwhile, I have a few examples below.
A simple example is Wikipedia: already the best encyclopaedia in the world, because it's created collaboratively by a critical mass of people that care enough to make it what it is.
Try also Digg.com: a news carrier which is fed information by the general public; items in turn are given prominence according to popularity.
Blogging is also, of course, another example of interactive collaboration. Enthusiastic bloggers on this topic include Luis Suarez and Edmon Begoli. (But of course, without sufficient readership and interaction, a blog is just a soapbox - like this one :)
Meanwhile, Matt Moran blogs a criticism of this: that social isolation is growing, and we need more face to face. But it's horses for courses really: a) yes, direct contact is important, but b) technology is providing additional avenues for communication - Web 2.0 is not a replacement for face-to-face, but an additional mechanism. Like the phone. Some people are isolated anyway, and technology helps break it down.
Again, I feel critical mass is the key. Smalltime info sharing and collaboration have limited uses, but when it explodes, the effects are awesome.