Actually, this is becoming fairly common practice - many people are buying an LCD TV and using it as their monitor. I personally have a setup like this (with a Samsung Series 5 32"), but there are a couple of drawbacks.
- Color fidelity - for some reason, the Samsung Series 5 does not seem to be as contrasty or vibrant as my main computer LCD monitor, a Dell 2407WFP.
- Eye travel - Anything upwards of 26" and your eye tends to travel if you are sitting too close.
- Sharpness - again, bigger screens but same resolutions means the dot pitch (or individual pixels) are spread out more, giving the impression of less sharpness.
If you are using it for gaming or normal stuff, I'd say an LCD TV as a monitor is really nice and big, especially when paired with a set of wireless keyboard + mouse. However, if you are going to do critical photo-editing or etc, you might want to invest in a good LCD monitor instead. Just my $0.02 worth.