Computer monitors are designed for computers. It's a personal preference, but there are reasons why you should or shouldn't.
TVs have poor pixel density. A 50" TV will have a 1920x1080 resolution, but if you sit close to it you can see all the pixels and it looks terrible. You have to sit far away. You can buy a computer monitor that's 23" and get a 1920x1080 resolution, and it'll look a lot sharper. It's common sense, really. The more pixels you can cram into a smaller display the better it'll look. The second huge disadvantage to using a TV over a computer monitor is the input lag. TVs have horrible response times. If you want to use a TV to game with your PC, you'll have a bad experience. A monitor will have a much lower response time, allowing games to be much more playable.
Computer monitors also come with better color reproduction out of the box, but you can configure a good TV to have just as good color. Using a TV with a computer is good if you're watching movies, though. But you'll probably hate your HDTV every time you have to use your computer for anything other than watching a movie; at least, that's what I've experienced. I have friends who love using their TVs.
For me, however, I don't like using a TV as a display because I want to sit at a desk, not on a couch. I'm not about to plop a 55" Sony BRAVIA on a desk, so I've got a 24" IPS monitor with a 1920x1200 resolution. Expensive, yes, but it's worth it to me.