If you have the need of dealing with other operating systems, you can use either Parallels or VMware Fusion to run an OS full screen on one display while your mac apps are on the other. This can be even more fun if you use spaces.
On my iMac at work I usually have space #3 a full screen Ubuntu linux on one monitor (the iMac built in) and a full screen windows xp on a 20" cinema display.