I actually use all of these sites. My Space is good to showcase your work if you are an artist or musician, I agree. I initially used it because everyone was on there, nowadays I just use My Space to put up pics of what I am watching, reading, thinking about. I probably should just replace it with a blog.
Twitter is good for news feeds, I get all of my news on there in one condensed area, I can read my college newspaper as an alumni, NPR, LOLcats, CNN, even Slashdot, I actually just set it up to try out this site.
Facebook is for all of my college and high school friends because everyone migrated to that site now, and they don't use My Space anymore. It doesn't have much value except that everyone is on there, that's all.
I mean a lot of the people on here do the same thing it is just all gaming most likely. You would probably spend more time gaming than seeing what your friends are up to online. Just an observation.
I also agree these sites waste too much time! I wish there was a site, where I could have all of these things in one, news feeds, status updates, instant messaging, blogging, showcasing art and music where everyone I know is online, plus games I like. It would make everything a lot easier and more condensed. It would the Walmart of websites, LOL