I used to use a 26" HDTV and it worked fine for most things including gaming. However, there was some blurriness to font, which made web browsing and RPG/MMO gaming hard on the eyes. It could have just been my TV, so take that with a grain of salt... however I know this is still an issue with a lot of people who use their HDTVs as monitors. Also, HDTVs are usually meant to be viewed at a distance of at least 6 feet, not 6 inches - so you may see some issues there. On that same note, having a 30"+ TV a few inches from your face might be a bit hard to use in general, unless you can put a bit of distance between you and the screen. It may be hard to see everything that's going on when you're having to use your peripheral vision all the time.
In my opinion, if you're only going to be using your computer for watching Netflix/Hulu/Amazon/etc and gaming that doesn't require much reading, then you'll probably be fine. If you're into programming, writing/word processing, or stuff like that, you may want to stick to a dedicated PC monitor.
