Doesn’t perform badly, I’ve been using it recently with Ruby code, and I like how it colourises the code to make editing code easier, and performs it auto-completion and method lookup (basically all the features you’d expect with a modern IDE).
It’s does’t startup as fast as using Emacs, or vi, but I find the features very handy and very convenient. It doesn’t look bad either. It runs better on my PC at home running Debian Linux than it does on my PC at work running WinXP. This is probably because I’m using a 1.5 JVM on WinXP and a 1.6 JVM on Debian. Running on 1.6 JVM’s means that Netbeans will automatically use anti-aliased fonts if you have anti-aliased fonts enabled (much easier on the eyes if your using a LCD screen).