But, happily, the app seems to function as it used to. I am glad I did it, I am not sure I would want to do it with a huge application. If I was starting a new application I would definitely use Tapestry 4.0.
My impressions are these: The changes to the .html templates are pretty much non-existent (no surprise). The changes to the .page and .jwc files are all welcome and will making life easier for me and easier for new adopters (so, easier for everyone). The changes to how services work are nice because they handle parameters better, but, otherwise the changes are neither here nor there — you just code them a bit differently and figuring out the magic the first time was tricky. Overall, I would say Tapestry 4.0 is worthy the upgrade, but, don’t start it on a big existing application.