Are you set up for a monitor? Not just a desk, but also for duplicating speakers, etc?
I plonked a desk in the rear corner of my front room and put my PC there, so I can use my monitor on the desk in front of me with the big TV on the front wall, so that (in my field of vision) the right bezel of my monitor is touching the left bezel of my TV. This means I can play PC games while watching TV, or use a long HDMI cable to throw PC games onto the TV for a change, or put 360 games on my monitor, and so on.
Nice HDTVs are OK, but... 1080P? In my opinion, 16:10 makes for a much better experience. And even 360 games can look so much better on a decent monitor.
So I'm in favour of having a PC monitor - provided you can manage to set it up so that it's genuinely useful. If you're only going to single-task or don't have space for a desk, then your decision is basically made for you.
(Also, I'm not the only TV user, so a second screen definitely comes in handy when the soaps come on!)