As far as I know, there are no major language changes... desktop developers see a few minor additions, most notably a new Console class which hides all the nasty details when building console applications (those running from the command line), ability to add/remove icons from the Windows system tray, a native (fast loading) splash screen etc.
Otherwise they've enhanced some other APIs like the SOAP client, and for some reason included a basic HTTP Web server (which although I can forsee will be useful for a project I'm working on, I would have preferred it as an extra download and not part of the core SE platform).
There's nothing majorly new to learn like generics and enums if that's what you mean...
Charles Lyons (SCJP 1.4, April 2003; SCJP 5, Dec 2006; SCWCD 1.4b, April 2004)
Author of OCEJWCD Study Companion for Oracle Exam 1Z0-899 (ISBN 0955160340 / AmazonAmazon UK )