Obviously I have knowledge of what these technologies are and I've had experience with their predecessors as well. As someone who has designed web sites for people and looked closely at WHY you would want to put you or your business out there, I think that Web 2.0 technology is a mixed bag.
One of the main attractions to the average person seems to be that it's quick and easy to get yourself out there on the web. Prior to this you would have to create a web site from scratch complete with layout, graphics, navigation and even embed any tags or search engine features you might need. With this technology, all of that is already prepared for you and it's easy enough to fill in the blanks. On the other hand, many of the blogs and social networking sites you find on the web look very much alike. They are meant to be cookie cutter simple so that anyone can do it. Not very unique or customizable. A few years ago web designers were talking about how a web site is all about CONTENT. You can have the prettiest graphics and wild animation and sound but what is your site without some good material inside? The result: loads of content in Web 2.0! It's almost nothing BUT content. The key to the whole thing now seems to be finding and sorting through all of that content which is where many of these tools we are looking at come into play. Now obviously there is good content and bad content. Who decides what content is put out there? Nobody! That's right, it's a free for all. So anyone with a connection to the internet can post all day long about Paris Hilton's prison hotel room. They can even be joined by millions of others who share the same interest. Scary! Thankfully we can control what we are looking for but I believe that slogging through too much irrelevant junk when searching for something important is a big turn off for most people. When it comes to research and using Web 2.0 for library purposes, this might be a big obstacle to overcome. After all the quality of the results are what is most important in that regard.
I have something for you to consider: Why are almost all of these Web 2.0 tools, blogs, youtubes and similar services FREE?