Ok, just did some testing.
At 600mhz, Runescape works. But its at <1fps, and takes a bit longer to load.
Still, might be worth messing with, just to see.
I also tested the BFS kernel-power version; It crashes the JVM during loading for whatever reason. Normal kernel-power(with CFS) works fine.

I just tested FreeCol. It "works" also, but performance is pretty poor(not very responsive). I assume its due to the OpenJDK version not being optimized for our ARM version. If someone can go ahead and make an optimized OpenJDK package, I'd be greatful.
If you want to test FreeCol yourself, here's what I did:
1. Download the .jar file from FreeCol's website.
2. Run it, note the folder it extracts things to.
3. Copy that folder to your N900(lets say you put the files inside ~/MyDocs/FreeCol)
4. Open a terminal, CD to your FreeCol directory, and type "java -jar FreeCol.jar"
5. It should launch. Intro video didn't play for me though.