I've been working with Tapestry 5, for a few weeks now, and I'm loving it. It's a big step up from Tapestry 4 and I think it could become a realistic competitor to Ruby on Rails. It has similar characteristics: convention over configuration and an almost religious devotion by its creator, Howard Lewis-Ship, to driving out duplication.
Sometimes he possibly goes too far. For example, if your page class is
/article/ArticleEdit the duplication of the word "article" is removed from the URL, so the URL becomes
/article/edit. It seems like an improvement, but actually introduces ambiguity and has caused confusion, judging by queries on the mailing list.
At the moment, you'd be taking a risk using Tapestry 5 in a production application. It's still "alpha" and unstable both in terms of the API, which hasn't fully settled down, and in terms of defects: There are lots of minor, and a handful of more serious, defects reported in JIRA. But if you're developing a non-mission-critical web application you might want to give it some serious consideration. It's already very good and only going to get better.