There was a permission issue with the Windows binary. I fixed that a little while ago, which enabled people to run the windows client. We are aware of the crashing client and are working on a fix. As for the account preferences problem, I have no idea why it will not let you opt out. For now I have canceled all of the beta workunits and I am working on fixing the account preferences issue.
We have never intended to force anyone to do beta testing! It is supposed to be opt-in and I am surprised to see so many people have opted to run the beta. I do not plan to run more beta workunits until the account preferences issue has been fixed.