I don't think 500+ open support requests, in and of itself, is something to be concerned about... it doesn't necessarily mean a lot is going wrong all of the sudden.
Perhaps several thousand new users have been added on the 777 promo. That may translate into scores of people every week who don't know how to use the webpanel, access their new ftp account, or transfer/register their domain.
This is in addition to the legion of previous DH users who have their periodic requests into support.
Do I look forward to to having additional support staff? Yes. Am I overly concerned right now? Not really.