The card, when combined with Windows Media Center (Vista Home Premium), really opens up your computer's capabilities.
The picture quality is TV-quality unless you're stretching it over a very large computer monitor - a regular TV's image is only a small portion of a modern computer screen and so you can see how ordinary TV is quite low quality when you begin to put it on a plasma or large computer LCD. That said, at 1600x1050, which is akin to stretching conventional TV to HD sizes, it looks alright.
One problem for me is the sensitivity to poor reception - on a normal digi-box its fine, but these tuners seem to really need a good signal.
That causes another problem, Media Center or the card's driver, can just hang when the signal is very poor. The signal doesn't break up like with a normal set top box, it just skips large chunks of time. Every now and again, as it skips, it hangs and you need a reboot. This occurs about once a week.
But this is fine when I consider that I get Sky+ style service over digital terrestrial, and I can click a button and play some music or show people my holiday snaps all while we sit on the sofa.
Add an XBox360 and you can stream it into different rooms!