I've always had problems while working with Resin 3, but with the recent work on Feature Types (allowing one to move attributes up/down and deleting them), Resin 3.0.7 completely freezes after about two operations and does not provide much info. Haven't tested this with earlier version of Resin 3.X, but it works fine in Resin 2.0.13 and Tomcat 5.
Previously I've found that Resin 3.0.4 and 3.0.6 occasionally freeze up for a a request (but if I hit back, and submit a new request it keeps going)
So I'm using Tomcat 5 for now.
Richard