Lion is the first OS X upgrade where I've ever considered whether it was "worth it" or not. This coming from a pretty deeply-rooted OS X fanboy. End result: I upgraded, I'm not sorry I did, it was worth the $30. There are some quirks in the UI that I don't like but can live with, but the benefits for me (iOS 5 SDK, iCloud) outweigh the quirks. As far as stability, it's no less responsive or less stable than Snow Leopard for me.