If you build a closed ecosystem, you and you alone are responsible for its value. As with other forms of leverage, you win on the upside, but there's also a lot to lose going down. LinkedIn is a closed, walled garden. It's gotten increasingly obnoxious (enough so that I've pared my legitimate profile down to its bare bones, and have a spoof one I use for research). And, well, we've seen any number of walled gardens implode spectacularly.

Logged into MySpace recently?