I spent the last couple of days upgrading AppFuse from Tapestry 3.0.3 to Tapestry 4.0.1. While the integration isn't as clean as I'd like it to be, everything works and all tests pass, so that's good. I did post a few remaining issues to the Tapestry mailing list, but there's nothing major. While the upgrade was frustrating (it took me 4 hours to figure out I needed "validators" instead of "validator"), I feel I know a fair bit more about Tapestry now. Furthermore, my experience on the Tapestry user mailing list was incredible. Yesterday, for every question I'd send, I'd get 2-3 replies in a matter of minutes. It was like having my own personal Tapestry consultant by my side. It goes to show that Tapestry is a thriving community, with a lot of folks willing to help out. Thanks guys - I really appreciate the help.
Update: You can view the FishEye Changelog to see what the upgrade entailed.