The switching costs for facebook are much higher than the switching costs for looksmart or excite. (I had/have an excite email - switching sucked) Also - all

The switching costs for facebook are much higher than the switching costs for looksmart or excite. (I had/have an excite email - switching sucked) Also - all your list of sites really shows is that some sites were able to grow and adapt with their audience (see Yahoo) while some didn't. Going on past performance - facebook is in that category.