Most people who develop for Google App Engine for Java use Google's Eclipse plugin. It makes it trivial to create a new App Engine project and dist it to the live servers.
The plugin is fine, but Eclipse is a whole different subject. I've been using IntelliJ IDEA since January and have definitely been spoiled by it. After IDEA, going back to Eclipse feels like taking a step backwards about 5 years. Plus, the JSP editor would crash on me after 10 or 15 edits, and the only way to fix it would be to close the file and reopen it. Seriously I couldn't fix that after many attempts at customizing my settings, it was just horrendous.
I haven't tried using their release tool yet but even if I have to release by hand, it will be worth it to be using IDEA again.