I've got an older 17" Samsung at 1280x1024 on the left and a 30" Dell 3008 2560x1600 in the center. Then I've got the PC also providing signal to a 1080p Panasonic projector that's on the other side of the room. I'd love to have 3 x 30" monitors (why not all 3D ready, too?), then a couple of new state of the art graphics cards.
But for any kind of work I'm doing at my place, I've got decent screen real-estate already. 3 screens side-by-side together, for me, would be just for gaming.
So, I might see how the gaming field evolves over the next few years before I jump in with new gear. I mean, I'm even getting by ok with my 9800gtx+ cards in SLI, so lately I haven't even been in a hurry to upgrade those.
But 3 monitor gaming and decent 3D home entertainment gear looks interesting, the games/3D movies are going to be out there, so all that could start to become more commonly used over the next 5-10 years. So, I'm certainly not turning up my nose (I also wouldn't be surprised if the monitors themselves, in the next decade, start selling as long, curved, one-piece units that give you a 90 degree field of view in 3D)