Hmm, I game on a 50" plasma TV at 1080p, and it definitely gives you that immersive feeling - not quite like a 3-monitor Eyefinity setup, but much better than my Dell 2707 monitor. Of course, I sit about 5 ft. away from the monitor, not across the room 😛.
However, text doesn't look that great on the TV so I would not use it as a primary monitor - good for graphics only...