Liked_Best: The people, very interesting to get faces and \"real-life\" personalities to put to names that you only see in bugzilla and newsgroups.
Exhibit_Hall_Hours: I think the current hours are ok, but there should be more room left to check out the exhibits, possibly with extending the lunch break on one or more days.
Improve_Next_Year: One fun event of a recent JavaOne was a \"Collections trial\", where Josh Block and some other guy were made to \"stand trial\", answer questions from the audience and generally \"justify\" the java.util.Collection framework (a very debated framework that they designed and wrote). Since exp. Block is very outgoing and verbal (and skilled) person, it turned out to be a great session with a lot of questions being answered and question marks being straightened out. A similar thing could be done for any of the core components (SWT would be a good candidate ;)