10.1 rocks big-time. On the release date, I swung by my local CompUSA to see what was happening and found the Mac section with more people in it than I had ever seen before. They had run out of the boxed sets of OS X and the rep was frantically burning free 10.1 update CDs for anyone who cared to have one.
I hung out a while, helped out a Wintel user who was trying to network his PC and his iMac, bought a couple of X-ready games (Alice and Tomb Raider Chronicles), snagged my CD and left.
Upgraded my tower when I got home and tried the DVD player. Rock-solid and smooth as silk, even when playing a couple of Quicktimes and running other apps. It didn't skip a beat.
The performance increase is very apparent. My WallStreet 250 was barely useable under 10.0.4 and now with 10.1 is quite snappy. My dual G4 Tower, on the other hand, was zippy under 10.0.4 and with 10.1 is amazing.
Both machines have been rock-solid stable under X, which to me has been the greatest benefit of this OS.