I could be Mark's twin. I have exactly the same situation at my vacation house: an HT1000 connected to an apple router (which connects to another one which distributes to the house) It will randomly hang about once per day (though just did twice in the last hour). This has been going on for several years. It sounds like there is a software patch that will improve this. How can I get it?
Yes, Chris (I think it was Chris) had their IT people push some software or firmware fix to our modem supposedly to allow it to work better with the Apple Airport Extreme router. It seemed to solve the problem for us. It has been working fine now for months. Have never had it disconnect when we aren't there since then.
Were you also having speed problems? I have an Apple Extreme and a HN9000. The modem reboots itself out of the blue and my upload speeds are super slow. TestMy.net says 92 % of tested systems have upload speeds greater than mine. Not good.