Customer oversubscription levels

This might be a dumb question, but I can be sure that I'll be told if that's the case, so here goes: What's a good oversubscription ratio for customer traffic to global Internet bandwidth these days? I.e., if you have, say 90megs of bandwidth to other transit providers, how much bandwidth, in aggregate, are you selling to customers -- 90? 450? 900? Do customers care about this? Or do they assume that if they get a T1 to the Internet from you that they have their own T1's worth of non over-subscribed bandwidth to your transit providers? Thanks, Mathew