I found this wonderful map over at Confused of Calcutta (the original is here), where JP Rangaswami has some interesting reflections about it. Here's a few highlights, but do read in full:

One, it represents many generations, but the generations are often isolated.

Three, we need to understand more about the places where the generations meet.
Why that is the case. Facebook and YouTube both span multiple generations now, Flickr and last.fm have that effect as well, but I find places like DeviantArt far more intriguing. What is it about the communities like DeviantArt that they became ageless from the start? What can we learn from them?