Although it's already been out for two weeks, it's only just now that I've had time to play with the latest July CTP drop of WPF. And I find it to be faster than June CTP, and in many cases it doesn't have to refresh the entire window when redrawing. I love it! Good job, team Avalon. Hopefully RTM will be soon.
One annoying thing: if you want Visual Studio support from Orcas then you have to have previously installed the June CTP, then Orcas, and finally upgrade the .NET Framework to the July bits. If you just install July CTP and then try the latest Orcas, it doesn't see the right .NET 3.0 framework on the system and halts.
One more annoyance: XamlPad is not compatible with this build, so you won't find it in the July SDK. But you can use Charles Petzold's “XAML Cruncher” tool to do the same thing! (Click-once deployment from the link.)
After playing with this stuff for awhile is it too forward of me to say that another name for WPF could be “Web 3.0”? :)