What prevented me from using Playframework and going with Lift:
1. Play 1.0 (2.0 too?) used exceptions for flow control. I don't think this works for high traffic web sites.
2. Lift's CSS selector templating is slick, I would not like to go back to PHP/JSP/... style templating.
Very nice website.
[update: 2.0 has no more exception work flow]