Allowing for the fact that the auto-redeploy facility isn't that fine-grained, there's too much chance for problems due to things like static elements within the jar's classes. That's been known to cause problems even with less ambitious attempts to do hot updates.
An IDE is no substitute for an Intelligent Developer.
Oh, I'm not. I've been playing with NetBeans Lookup in Tomcat, and I was hoping I could pair the two to get new functionality without having to bounce the app. Lookup can monitor the classpath for the addition or removal of classes which implement a specific interface. I didn't figure it would work, but there's no harm in asking.