I have tried to post a couple of videos from Vimeo over the past couple of days, and all of them failed to validate. I know I successfully subbed a clip from Vimeo recently, but I can't remember if it was pre-3.0 or not. So, I'm not sure if this is a Vimeo issue or a VS 3.0 issue.

Also, the embed code looks a bit different than it does in the submitting videos page. Perhaps they changed their embed code? If they did, would that cause the submitter thingy to reject it?