I'd like to agree with Patrick, because that is my natural tendency when I see a project that everyone praises. But I know better. I think it's better not to speculate on the productivity or usefulness of a framework until you've used it to develop an app.
That's what I did with Spring, WebWork, Tapestry and JSF last year. Now I feel like I know "the truth" and whether one framework is better than the other. The truth is they all have strengths and they all have weaknesses. While one might work well for one project, it might not for the next. I think the best thing is that you don't setup yourself for framework lock-in. If you only know one web framework for Java, you should probably pick up a book and develop an app with another framework - just to see how things are done differently. Now that I've used all of the Big 5 in Java, I don't think it would be that hard to migrate an app from one framework to next.
So what am I trying to say? Don't bash on a framework until you've tried it. And I don't mean toying around with it on a Tuesday night, I mean using it for a real-world project. I'll probably diving in and doing a little Rails development later this year. Why? So I can see if all the hype is accurate.