Hi there!
Here is my first entry to the 4K contest… It’s a remake of the old Pipe Dreams… Any suggestions and criticisms are welcome. It includes a micro sound effect (but if audio initialization fails it will proceed without using it), but I preferred to invest bytecodes in the game mechanics and visuals rather than in sound.
This is the first 4K program I wrote, ever, and I came upon quite a few surprises. I hope to improve with my next entries, which will be more action oriented 
Webstart : http://www.ahristov.com/tubedreams/tubedreams.jnlp
Instructions : http://www.ahristov.com/tubedreams/
Screenshot:
I don’t notice any difference in the computers I’m trying it, though (it gets at most about 45% of CPU usage on WinXP + Java 5)… Could you please test it again now? It’s currently yielding for 30ms on each game iteration.