I feel like I'm less productive on multiple monitors. I've tried them a number of times, but they've never felt natural. I just prefer looking straight ahead, managing a single screen, and clicking between the few programs I'm running in the taskbar. Also, I like some room on my desk, and big monitor displays just seem overwhelming.

Screen resolution is important though, otherwise everything just feels cramped. I'm perfectly happy with a nice 23-30" monitor. Anywhere within that size range is fine, but it needs to be a quality panel. I work with a lot of very subtle colors, and light gray tones. With a TN panel they're invisible half the time, or I'm constantly shifting up and down in my seat trying to find the sweet spot for more accurate colors.

If I had to pick my dream setup, it would be a single 30" monitor. If Dell gets those 4K 30" displays rolling out, I'm sure they'll be great. For now, I don't feel like my productivity is suffering in any way with a 24" monitor.

Personally, I find I'm most productive when I have a nice clean workspace, natural light, and a good chair. For example, I just grabbed a photo off Google...

http://articlesofton.files.wordpress.com/2011/12/01-04_home_...

Replace the chair, and it's ideal for me. Bright light, and minimal clutter.