I tried my aging PBG3 on TV for gaming (Unreal Tournament) and I thought I had a new computer! Framerates above 60 become irrelevant (TV has 60 fields/sec or 30 frames), higher res becomes pointless (640x480 looked fine) and anti-aliasing becomes automatic simply from a TV's natural blur. Only problem: tiny text (like in-game chat) can get blurred out.
The "poor" quality of TV actually hid the defects that my 'Books native display would show, making my low-end 3D board look practically like live TV footage. I think that's part of why console games give such a good impression, actually.
Anyway, try it with a 3D game and you'll be impressed.
(Tip: do NOT mirror the display. Put the menu bar on the TV (may even be a needless step with some games) and let the internal display sit idle. Reason: with mirroring, the GPU actually processes the graphics TWICE, at least on my 'Book. So it's the opposite of what you'd think: spanning is actually FASTER for games. Sure, you're drving extra real estate, but the game's not rendering on the extra space and it doesn't hurt.)