What level of support did you have? I've been on developer or first-level business support, and generally get someone knowledgeable; only the timing changes.
The only bad experience I had was with SES - we got blocked by high bounce rate, sending to a test email that did not exist (specifically because it was a test email). It took two days for the special unblock team to unblock us, even though the general support guy I was talking to had responded a couple of times in that wait period.
