* Why do you start at 3 brands? I'm guessing that there are enough users that would like to monitor a single brand maybe for $12-$14/mo?
* The plan pricing isn't good. The Big Shot plan costs $100 for 10 brands/users while the Blogger plan costs $19 for 3 brands/users. Why shouldn't I just get 4 Blogger plans? Clearly the convenience of not having to deal with multiple accounts and who can access what where, but it just doesn't look like you're getting the value you should be getting. As 37s said about their pricing "Each tier is roughly double the previous tier, but we deliver more than double the benefits." (http://www.37signals.com/svn/posts/1287-ask-37signals-how-di...).
Overall, it looks like a great way for companies to track their brands online and see how things are going. I'd say you could easily create a sustainable business model out of that.