I have played it for some time (although not thoroughly).
In my opinion, Netbeans 4 has a nicer GUI compared to Netbeans 3.6. The startup is also faster (but still slower than Eclipse).
Out of the box, it is quite complete (GUI designer, Web app, integration with
Tomcat).
The font is BAD. And I think it is also resources muncher. And the option menu is something cluttered.
Yes it is a huge leap from Netbeans 3.6, but compared to Eclipse (for the responsiveness, etc), it is nothing special.
In general: I prefer Eclipse rather than Netbeans (for free IDE). But for really good experience, nothing can beat the IntelliJ IDEA (yes I know it costs some $$$$ ).
Just my 2 cents.