Plenty of people have dual displays. Some people on this forum even have dual 30" displays.
Depending on what you're doing, you can never have enough screen real estate. Dual displays for web browsing is overkill, but if you're doing programming dual displays can be incredibly helpful.
Personally, I would love 3+ displays for my web design. It would be great to have one for iTunes, web browsing, and previewing my site, another for text editors and Finder windows, and a third for reference, specifications, and e-mail.