Public previews are not supposed to be released for a month or so, but I downloaded a developer's snapshot build during my lunch break today.
Understandably, there are some rough edges (I was unable to get a new J2EE 1.4 web app project running), but overall, I am enthusiastic: the UI looked very good, "regular Java projects" worked well (super fast build and run time for small projects).
NetBeans 4.0 will have refactoring and full web application development support. I look forward to trying version 4 again in the near future.
From a few dialog boxes, etc., I got the idea that Sun's Java Studio Creator (which I have also been playing with - looks good, but the Mac OS X beta is a little rough) definitely uses the new NetBeans codebase -- fair game: support an open source project, and also customize a proprietary version.
With IntelliJ, Eclipse, NetBeans, etc., it seems like Java developers have an embarrassment of riches.