Up until now BBM 5.0 has just only seen minor upgrades with bug fixes and backend upgrades. Many users expect new UI and features each time an update is released but that has not been the case. We are not likely to see any new features and UI update until RIM officially releases an update. We have seen a few BBM 6.0 leaks but there has not been any noticeable changes.
A screen shot that surfaced today shows that you will be able to set a color preference for messages and also include some of the new 6.1 icons we saw from a leaked OS.
On a side note there is a 6.0 leaked BBM floating around but I would suggest not to try and install it because it will likely give you headaches and mess up your BlackBerry.