That has been my experience as well, to this day I have an ActiveMQ broker for which the JVM just stops responding, its not the broker that goes unresponsive, its the entire JVM, with no error, no log, no nothing, it just stops replying to the service wrapper and sits at 100% cpu usage. The wrapper kills that JVM and restarts it once every couple days because this happens.
Oh and this was fun: yesterday I went to check on the broker as it was running a bit slow, the DLQ had ~50,000 messages in it that were not there last week, all were timestamped to the same second in ~July 2012...9 months ago...
I'll likely never use ActiveMQ again.