Well, I had my doubts when I started, but I made it through to the 23rd thing. I am surprised at how much I enjoyed working on this learning project, and at how well it went! I learned that you don't have to be technical genius to do a lot of this stuff. I can see how someone could get hooked on these tools, especially if he had a lot of time to experiment. I don't know how much I'll use what I've learned, but at least I have a much better understanding of what web 2.0 is about.
The thing that might be my favorite and the most likely thing that I will continue to use is flickr. I also enjoyed Library Thing, del.icio.us, and of course YouTube.