I've been running the test-11 version for a few weeks now, just to see how things were coming. It took a bit to get up and running, but it hasn't presented any real problems.
I have noticed that many applications are running a bit faster. When I compiled a custom 2.4 kernel on this box, I noticed a performance gain, but mostly when X was not running. The 2.6 kernel, by contrast, has performance gains with X running as well.
Some interesting info on the new features for the 2.6 series can be found here:
http://www.kniggit.net/wwol26.html
and here:
http://www.linux.org.uk/~davej/docs/
in case anyone is interested. Have fun!