I have two monitors hooked up to my computer right now and it owns! I would do it again for no other reason than the ability to move my mouse from one screen to another:)
I once saw Harry Anderson (of “Night Court” fame) give the keynote speech at a small computer fair. He was an early adopter of technology, and had a small software company (not sure if they ever released any product).
Anyhow, one of the things he said was that everyone should have the chance to call their family into the home office so they can see you put your head between your dual monitors and drag a folder in one ear and out the other.
By the way, I’m totally jealous. I’ve always wanted another monitor, especially for Photoshop. You can have your image alone on one screen and all the palettes open on the other. Heaven!
Good god, how could anyone tolerate a computer with only one monitor? Stone knives and bearskins!
I like the way my laptop somehow knows that the Sony Trinitron at home is the secondary monitor (so the menus and trash can and desktop icons and drives go on the built-in TFT screen) but the Dell Trinitron at work–hooked up to the same video connector–is the primary monitor (so the Trinitron gets the desktop icons and whatnot); and how Eudora puts my workplace-related incoming mail folder on the auxiliary (TFT) monitor when I’m at work but hides it behind the personal inbox when I’m at home or running in single-monitor mode. And how Photoshop remembers how I arranged all those tools palettes on the auxiliary monitor and starts up that way, so my main screen is empty except for the current document!
Excel is a little less clever about it. I have a workbook for doing monthly finances. I have to keep three separate open windows for the same sheet defined: a narrow strip for when I’m at my girlfriends’ (no second monitor there), a full size window on auxiliary monitor for when I’m at work (aux on right), and a SECOND full size window on auxiliary monitir for when I’m at home (aux on left) – Excel dutifully restores the position of the windows to where I left them, never mind that sometimes those windows are on “phantom monitors” and I can’t get to them!
I like to use my 2ndary to hold all those displays that normally clutter up my primary–like html code, a fully expanded winamp, chat and so on. Very handy.
Only gripe is that opengl doesn’t accelerate with a 2nd monitor on–I need to disable it if I want to run quite a few video games. Annoying, but a sacrifice I’m willing to make if I’m to have the ability of having two separate visual channels for pr0n… 
I only have one monitor, but in linux I currently have 4 screens, though I could have many more if I wanted. Thats plenty enough for me, though.