Ubuntu and cable modems

The other day I was trying to help somebody on the Ubuntu forum get an internet connection. I didn't notice at first that it was a cable modem (of which I have zero experience), but when I did, I decided to look into how they work. (The thread is here.)
There seems to be a lot of confusion around as to how to get a cable modem connected and working with Linux, how to solve connection problems, and how to connect a different computer or a router.
Here are the myths:

• Cable companies only support Windows or Mac.
  
• You'll need to spoof the MAC address of the computer originally connected to the modem in order to connect another computer or a router.

Here's the reality:

• ISP software may only work with Windows or Mac, and technicians may only know about Windows and Mac, but there's actually no obstacle to getting a connection. A modem connected to a cable network needs to be "provisioned": the cable company needs to know the MAC address of the modem. They can do this at their end, or the cable guy can do it at your end. If it's done at your end, the cable guy will need Windows or Mac. If you have Linux, the advice is: just get the cable guy to connect the modem and tell him you'll call the provider service line to provision the modem.
• After connecting a different computer or a router to a cable modem, power down the modem for 10 minutes before connecting (the computer and/or router should be off while connecting too). Power up the modem> (router)> computer and everything should be fine (no need for spoofing). A good guide is here.

In Ubuntu, make sure DHCP is enabled unless the cable Internet provider has told you to use a static IP address.
The original poster at the Ubuntu forum thankfully managed to get his connection working, despite my fumbling around for a solution.