EyeTV is GREAT. I have both the EyeTV 250+ hooked to my iMac, and a EyeTV Hybrid that I take on the road with my MBP. Watching/recording is very easy and great quality, letting you program specific over-the-air channels/schedules to wake up and record a specific show.
You can certainly hook it to your dish/sky service, but the problem I've experienced with this, is that the channel selection must be controlled from the remote/box your cable provider gives you, rather than controlling it from the computer via eyetv. Over-the-air tv is controlled from eyetv, since it's also a receiver.... But when hooked to cable service: if you wish to schedule a recording while being out, this becomes tricky since the cable box must stay in the channel you wish to be recorded, so when your mac wakes up to record it, it plays that channel.
