In Activity Monitor seems that memory management is more agressive, so I believe it could be better, but we will see. I did not test a long time Safari web browsing with many tabs which is a significant problem in Lion.
The most significant improvement is a Safari 5.2 - faster than 5.1.5 and there is no need to use additional search bar. But I hope that Lion will get also a new Safari as an update.
Updates are now through AppStore Updates which is funny because in Lion there is a place for it, but not used in the same way like in ML. Do not expect much.
I did not test more features, but it seems that ML release is mainly because Apple must to adopt OS icons to new products with Retina display.
Anyway forget about benchmarks I do not recommend to use ML DP2 as a standard day to day OS. Wait for a ML final release. Still there are visible issues: (graphic artifacts) during boot and desktop use, animations are not smooth. Currently Lion seems much better choice even if not perfect.