Heh, actually, if you browse their site a bit you'll see that their latest models don't even require you to open your computer, they'll plug right into a USB port. And, since the device has it's own tuner, you can use it to watch/record a different channel than the one being watched on the TV, so long as the signal isn't coming from a cable box. If you have a cable box, then you have to tune the device to channel 3 and use the tuner in the cable box to change the channel, which means both the TV and the device will always be on the same channel (unless you have two cable boxes...)
The only real problem with using a device like this is the disk space it takes to record a program. With a "moderate" quality setting (I used the "extended DVD" quality) an hour-long recording takes up about 1.5 Gigabytes of disk space. The highest quality takes up twice that. And those are for standard TV... the one I have doesn't do HDTV, that would probably need even more space. So, if you plan to do much of this, plan on having a lot of hard disk space available!