Monitors are like boobs. They can never be too big!
Oh dear... I think we're going to have to agree to disagree about this criterion of female beauty (I'll pass on the discussion of manboob size).
The same goes for displays -- size alone is not an unqualified good. As Kalrith
et al have pointed out, there's a huge difference between the resolution, viewing distance, and utility of a 32+
television (probably 1920x1080) versus a 30-inch, 2560x1600 monitor. A big TV is like using a (more or less) conventional resolution display, but you need to sit further away owing to the larger / coarser dot pitch / pixels. Whereas, even at 30 inches, a 2560x1600 display has fairly small pixels (.258 mm dot pitch?).
A higher-res display will of course demand more processing power: you'll need a fairly capable video card to play modern games at that resolution. Even playing movies (especially if they're Flash) can be
rather stressful at such a high res. On a related note, as Mr Pedantic observed, it might be useful to be able to 'fullscreen' an app or window without having to drive over 4 million pixels.
Finally, such a size and resolution might improve your productivity, or possibly worsen it, depending on your workflow, apps, preferences and habits. Do you dislike having to move your eyes to a different portion of your screen? Does it help you stay sorted by having windows clearly spaced and differentiated rather than piled on top of each other? Do you require lots of menus and sub-workspaces (think of design / editing software)?