Today I installed JRebel because I was tired of all the Republish stuff when working with JBoss in Eclipse. I am glad I did! I am not sure how much time it saved me exactly (when working for 4 hours) but looking at the JBoss server.log showed the following:
Maybe a little too optimistic, but a republish costs one minute at minimum. At 40 redeploys, this saves me about 45 minutes. This is 1.5 hour for a full work day!