Right, the subscription/freemium model. But is it sustainable? Most of their users stick with the free service level, and as more and more startups enter the

Right, the subscription/freemium model. But is it sustainable? Most of their users stick with the free service level, and as more and more startups enter the fray, they'll be pressured to offer the same (premium) services for free. Remember what Gmail did to Yahoo's plan to charge web mail users for more storage space?