NetBeans 4.0 kicks ass
The IDE is more stable then 3.6 (i havent seen none of those nasty java.lang.arrayoutbounds erros when the intelligent code filler listbox thing pops up trying to load j2me classes...).
It compiles a hell of a lot faster.... yes its very slow to load the app, 30 seconds to a minute. but compilation speed is excellent. may seem slow to some but consider the app compiles, preverifies, obfuscates, packages, etc etc. its awesome.
Even John Carmack is using NetBeans:http://www.armadilloaerospace.com/n.x/johnc/recent%20updates/archive?news_id=295
(though he does complain about the ide being very slow)
runs fine on my laptop (1.8ghz p4, 512 ram) though makes the little fan spin annoyingly a lot.