So I've just installed the trial version of Mathematica 9. The first noticeable feature for me is the new built-in physical units. I used AutomaticUnits package before, it was almost perfect except that its units aren't usable inside many other functions. But new units can be used everywhere but I can't yet figure out how to implement new units and unit systems or override an old ones. It would be great to have a way to convert units to CGS system.