The developer Tool for Windows Phone reached beta-status! And Microsoft included Expression Blend 4 for Windows Phone into the 380 mb Setup. Get it here: MS Setup, but make sure to uninstall any CTP version before!
So far the good news.
Bad news are: several things have changed from CTP.April to beta – most of all: consolidation and Namespaces. MS advices to totally rebuild your projects, and just copy the content of xaml and xaml.cs files except the template-code.
It took some time, but I got my application running again.
See a detailed list of changes on this page: MS What’s new in beta version.