It's no surprise that the database schema and stored procs have undergone a significant overhaul in VC 2.5, but for me some of the kep improvements is with regards to the statistics collection levels.
In VC 2.0.x the statistics collection level was a single global setting, with Level 1 being the default and VMware recommending that anything above Level 2 was used purely for diagnostic purposes.
But with 2.5, the stats collection levels can be configured per rollup period, which is great! So the recommendation now is to use Level 3 for Daily and Weekly rollups, and Level 1 for monthly and yearly. That makes it easy to do reporting on things like CPU Ready Time without needing tera's of disk for data that is pretty much useless after a week.