Basically more screen real estate (2x 1280x1024 > 1920x1200 for example). For work, you can put different things on different monitors, like if you want "full screen" side-by-side comparison of code/documents, or your Email/IM clients on one screen and other work stuff on the other, etc.
For gaming, if you are running games like FSX, it supports multiple monitors. Some games may allow you to see the game full screen on one monitor and your IM/Teamspeak on the other (I can be wrong on this one).
The Model M is not for the faint of heart. You either like them or hate them.
Gerbils unite! Fold for UnitedGerbilNation, team 2630.