I currently have a 24" and thinking about getting something bigger. But how big is too big when you're sitting 2' away from your monitor at your desk? 32"? 37"? In my case, it'd be used for gaming and music production.
My suggestion would be go to Bestbuy or whatever electronics store that is near you and stand in front of various size 1080p monitors/TV's and see at what distance you can perceive pixelization. Just as an example I find that at about 6' I can see pixelization on my 50" TV. I use it as a Monitor for most purposes. I usually sit about 8' away.