I'm running it on my 2009 MBP with 2.66 GHz C2D and 8GB RAM, and its a dream! My MBP was already pretty darn fast since I take good care of it, in fact its usually snappier than my 2011 i5 iMac funnily enough.
Since installing Mavericks, animations seem a lot more smooth and apps are more quick to respond. I have yet to see any drop in performance and I've been using it a lot. I've run a ton of apps and seen almost no slow down at all. It tends to run cooler than ML too, with general CPU temp below 50 degrees when using finder, safari, mail and a few other apps.
Everything just seems more smooth and snappy, and its all very fast. I literally have no reason to upgrade my laptop any time soon.