Facebook very similar to Google in regards to their methods of growth. They add little things here and there frequently. If you look at Google they expand there apps like crazy... http://www.google.ca/intl/en/options/
...and facebook is following suit as they seem to add a new option every month.
I don't like facebook, I think there are just waaaaaaaaay too many apps it's almost too ridiculous. Worst of all, the number of apps invitation you get is directly proportionate to the number of facebook fans you add. You also can't do much with the page (esp. compared to Myspace).