I originally posted this little titbit in the wcf forums, but since lots of people there did not seem to know about it, I'll post it here again:
The framework 3.0 RC1 install will kill your existing .svc mapping, so you will not be able to communicate with IIS hosted WCF services (.svc). Obvious workaround is to add the mapping again manually. This will be fixed in the next RC.

I hope that helps a few people out there!

Just last Friday, I readied everything to integrate my winfx parts into our main application. I instructed the team on what to do and put the bits on our server.

Now, Microsoft released RC1. Just my luck, but I'm obviously very happy that winfx is progressing!! Get the new SDK as well. And, you're not hip if you're not running Powershell RC1, or use the word 'hip'