I'm hoping I'll be able to find someone at customer support who'll tell me something other than "Oh, the problem's your modem. It's broken. Just go down to the office and get a new one." I admit that it's possible that they're right and I'm wrong, but given that if I follow this advice I'll be on my fourth modem in six weeks, I kinda doubt it.
I'm very seriously considering getting my internet service and my cable turned off, just on general principle.