I have one in my HTPC and love it. Little to no pull on my GPU or CPU, low power consumption; does get a little hot sometimes but nowhere near GPU hot.
Restrictions: most tuners these days can pull in HD over-the-air (your local free stations) but getting Satellite HD is next to impossible. Cable HD is possible, but you have to jump though some hoops.
What kind of TV do you want it for? Cable, Satellite, Over-The-Air? Is HD necessary? Do you have ample storage space? A 30 minute show can be around 2GB, and a movie can weigh in at around 6GB.
Edit: almost forgot: do you know your PC well enough to know what (if any) type of free expansion slots you have? You can get tuners to fit PCI, PCI Express, USB, and even Express Slot for a lappie. (I don't recommend the USB version unless you simply don't have a free internal slot).