There is little question that Twitter is the second most popular social networking site on the Internet behind Facebook. As more and more folks “discover” Twitter and how useful it is the more popular this tool will continue to be. However, for the first time the (U.S.) visits have declined for month-over-month. That decline was an 8% decline for the month of October. Comscore estimates that Twitter’s visitors went from 20.9 million visitors in September to 19.2 million in October.

Now, let’s put this in perspective, Twitter’s growth from October 2008 to October 2009 was a crazy 1,271% growth and their global visitors are at 58.4 visits per month, so there is still a lot to be optimistic about. This could be part of the motivation for Twitter to release many of their new features like the retweet button, geolocation feature and their new lists, which are really cool.

Still, the big question I have about Twitter, and the one which makes it’s valuation crazy, is how are they going to monetize this? The valuation is at least a half of a billion dollars if you base it on the offer that Facebook reportedly made to them early in the year. I can kind of understand why Facebook would want to buy Twitter, then they own the market on social networking. However, Biz and Ev don’t need any money, they’ve already struck it rich. Still, I don’t know why anyone else would want it because I’m still not convince that this thing can make that kind of profit . . . or any profit. They have not so far.