Right now there is a trial going on with a 4 tuner DVR supplied by Comcast. Comcast promises it will become more widely available, but there is no reported dates set.
You have the choice to purchase a retail Tivo Premiere Elite with 4 tuners and a 2TB drive. If your a heavy DVR user and can afford it, this is a premium DVR that you will be happy with. Purchase the Tivo, subscribe to Tivo's service and then add a cable card from Comcast at the monthly rate. Right now a Tivo doesn't do On Demand, but it is coming to Comcast subscribers and Tivo has it's own online content available from 3rd parties such as Netflix, HulaPlus, Blockbuster & Amazon.
Other users are using a cable card PC tuner in a Windows Media Center PC. These have 4 tuners to record to the PC. You can have a Media Center PC hooked up to your HDTV or use a Media Center extender such as a Ebox on your TV to watch the recordings. Cable card tuners are from Mfr's such as SiliconDust, Hauppauge and Ceton.
When you're looking up shows to watch and you push the button for more info,do you notice the little clock icon in the menu? Usually if it's not on a major network,that little icon will show you other times a program may be on? That way you can schedule your programs appropriately,so you don't miss anything. I'm more of a movie and History channel type watcher,so most of their schedules are flexible,when setting up recordings on my dvr.
I think the top of the line TIVO boxes can only record 4 programs at a time? Hey but a Comcast customer can always dream,huh?