The theme of JavaOne 2006 is Java EE 5. However, it there was an unofficial theme, I'd have to say it's NetBeans - the tool is simply EVERYWHERE. Therefore, I shouldn't have been surprised when I was browsing through the JavaOne Book Store and noticed this post on the cash register:

Mixed among the other hot topics of the year - EJB 3.0 and AJAX - you see the NetBeans IDE Field Guild. Congratulations to Patrick, Ludo, Greg, Charlie and Chris for putting together a great 2nd edition to compliment the 5.0 release.