There is a brand new version of JBossMQ coming out the 1.0 that has dramatically improved performance.
Another possibility is that you are missing something, never understimate the power of silly users...
I'm running the new JBossMQ 1.0 beta, and the performance is much better than it was before. However I still see that sends to a Queue are about twice as fast as gets from a Queue. Is there a reason for this? I'm still pretty happy since my message throughput is between 1-2K messages/sec, but a 50% performace decrease seems like a lot to me, for no apparent reason.