I really like the idea and overall a pretty good implementation for a first go around. GPU Mining support would be a huge plus, but improving the performance of the current CPU mining implementation really needs to be done.

Using your site, my Core2Duo 2.2ghz gets about 660KHash/sec. Using Ufasoft's SSE2 miner, it gets ~5,500KHash/sec. I know that you are using Java and so can't exactly write to the instruction level of the hardware, but there should be some sort of optimizations that can help out at least a little bit.