Having already signed off on the PDF pages of about 90% of my WPF book, I was hoping that the June CTP would have a minimal impact. No such luck. The second program I recompiled under the new build revealed that the default dimension of a GridSplitter is now 0. The implication: If you don't explicitly specify a Width or Height in your GridSplitter, it'll be invisible.
Just this one problem (and I don't know how many others I'll find) has me worried and scared. Every program and every code snippet with GridSplitter has to be fixed, and making extensive changes like this after chapters have been paged is very dangerous.
Today I briefly enjoyed a mini nothing-to-do-on-the-book vacation. Tomorrow I'll be dealing with this disaster and hoping I won't find any others.