I noticed an interesting change in most of the 5-man encounters I've seen in WotLK: Boss encounters are based more on timers than percentages. For instance, adds are summoned every X seconds rather than at every 25% health.
I don't know if this will translate to raids as well, but it's a welcome change for the 5-mans. By getting more gear and more skill and killing bosses faster as a result, the encounters become notably less frustrating. It will be a nice way of pushing DPS to perform their roles better and will be a good benchmark. I can't wait to say to some unsuspecting DPSer, "we got three sets of adds this time? Ouch!"