I was just wondering as a point of interest, how often have you guys tried to return a work unit or get new work, and it comes up with the server busy error (503)? Cause it seems like at least once in every 3 or 4 WUs, maybe even more.
I get that sometime, but not as frequent as what you describe. It depends also on the client you are using (you get assigned to different servers based on the client).
You might want to check Folding Forum • Index page to see if other people have reported the problem with that particular client or with the server to which your client is trying to connect.