Here's an interesting post from Slashdot (posted by /. user “stwrtpj (518864)”) that outlines some good pointers when making a cable modem tech support call:

The key to working with Comcast is to have some basic technical knowledge of cable internet. Once you show you know the lingo and you know the basic technical aspects, you'll either get the support person to “talk up” to your level immediately or switch you to someone that knows. Most support people have at least heard some of the terminology, usually enough to know if they're in over their head and need to route you to someone else.

For example, if you buy your own modem, NEVER say “I need my new modem INSTALLED.” Say “I need my new modem PROVISIONED”. 95% of the support people will know right away what you need and won't bother asking you about Windows and you'll be online 15 minutes later.

Know how to get to the status page of your modem (usually http://192.168.100.1/ [192.168.100.1] but may vary depending on model). Know that your downstream signal needs to be between -10 and +10 dBmV. Know that your downstream SNR should be above 33. Know that your upstream power should be between +30 and +50 dBmV. When my signal dropped because of a splice in the line gone bad, I didn't tell Comcast “my internet don't work”, I told them, “my downstream power is -16, which is out-of-spec, I need a tech to take a look at this”. I had a tech out the very next morning and was back online by the afternoon.