I saw a Bill Buxton talk in 2004 or 2005. In it he said that within six years computer monitor square footage would be cheaper than whiteboard square footage. I'm looking forward to year 2011. This may be true. I've always been a fan of big screens (actually, I'm a fan of big screens on the desktop, small screens for laptops). Recently I found that a study was done showing that big screens really help your productivity. You could be 52% faster.
Right now I have a decent-sized screen, turned vertically. The screen can be turned in any direction, but for the most part I keep it vertically oriented. Here's why: most of the stuff I deal with is vertically orgainzed: email, documents, programming. The only things that a horizontal monitor are better for are watching movies/videogames (which I don't do at work), and certain webpages.
However, it's been my dream now, for several years, to have a huge monitor. I mean like wall-covering. If you think that sounds like too much space, think about why a big desk is better than a small one and you'll start to understand. It's easy to processing and understand things when they're spatially organized.
Big monitors are expensive, so I've been holding back. I'm thinking of getting an additional monitor to put beside the one I have.