I don't know anything about the internals of the alternative JDK and seen as it's available free now I don't have any reason not to try it. We have reasonably good test coverage. A lot of the applications on the server are groovy and grails based.
I am considering this because I've switched to using it for running all my local workstation applications such as intellij and builds and it appears to have made quite a difference. I have to admit I haven't been particularly clinical about my tests though admittedly.
Perhaps it is because things like in IDEs and builds are very I/O intensive as apparently this is one area where jrockit is quite different.