I was reading through Matt's rundown of Struts 2 (does it suck?) and he strayed into one of my most passionate areas: feedback.
He gave an example of an incorrect property name, and how that would be reported to the user. He showed examples from all the major frameworks, and the Tapestry 4 version, even without its proper CSS styles, won hands-down.
However, as I was reading and responding, it struck me that while other framework can barely tell you what you've done wrong, Tapestry 5 should be telling you how to fix it. In this case, advising you about the possible properties you could have specified, which I've added as TAPESTRY-1737 and fixed.
Here's the result. Not bad for ten minutes work. And remember: property names in Tapestry 5 are already case insensitive, which wipes out probably 50% of your typical typing errors anyway.