What's not mentioned (it's hard to sell) is, 50%+ of the reason Lift is so fabulous is, you're writing Scala. It's a mighty upgrade in quality of life, from either Ruby, Java or Python.

By corollary, what's being omitted is, the learning curve is steep. Scala isn't super-easy, and Lift dives fairly deep into the more complex stuff - implicits, currying, etc.

Nor is Lift itself all too well documented just yet. Yes, there's two books and a super-helpful community, but the experience is still in a different universe from the lavishly over-documented Spring MVC where you never really have to ask a question.