I suppose it was bound to happen eventually, but a federal judge just ordered Google to turn over the viewing logs for YouTube (your usernames, IP addresses, etc) as part of the current Viacom v YouTube and Google litigation. The EFF is fighting this, of course.
But, this doesn’t bode particularly well for privacy and the use of SaaS-type computing (ie: putting your data into someone else’s hands for whatever reason) given the way in which the court interpreted existing law.
PS. Deleting your account at this point might not help… but I would definitely recommend re-evaluating what you have as your YouTube (and other services’) username and if you use your real names in the profile information. Just a thought.