The web these days is full of applications that do cool things but don't provide a hint of value to end-users that makes it worthwhile to pay. One suggested option for Twitter to monetize on was charging for premium membership (http://calacanis.com/2008/01/02/the-three-business-models-th...), the one option so far that seems to be in line with traditional business models: provide a service that people are willing to pay for. The blog post suggests 1-5% of users might subscribe to some kind of premium membership...I think more along the lines of 1-5% of active users, which drastically cuts the number of potential subscribers down. Bottom line: advertising might be Twitter's only hope, but I predict limited success (in the long-run) unless Twitter finds a way to produce a service they can put a price tag on.