I disagree, I use emacs with vertical splits (ie 1|2|3 layout) and 16:10 and 16:9 is great for that, also it means that spreading over onto the second (16:10) monitor isn't a change in layout policy.
I could never go back to 4:3 layout for programming, as I discovered last year when one of my 16:10s died and I had to use an old 4:3 I had laying around.
In my experience using a small monitor with X configured to use a virtual screen (i.e., the monitor just shows a small part of a much bigger desktop and you can scroll it with a mouse) is just as good as the giant monitors. I don't feel I really gained that much using 30" or 2x24" in comparison with the 15" monitor and 2000x2000 pixels virtual window I used to use in the past. Of course it's hard to argue that large monitors aren't nice, but I think the benefits for writing code are overstated.
Apple IMHO has done much better with the widescreen format than Windows has - the UI paradigm does not encourage full screen use.
Look at, say, Visual Studio - the thing is practically unusable without being fullscreened (unless you enjoy 200 pixels actual code editor). I've always felt widescreens to be a bit useless on Windows in that regard - the overfocus on fullscreen apps robs widescreen of its primary strenght: multitasking.
I use a 2-column layout on a 30" Apple Cinema display. Each of the columns has a 4:5 (8:10) aspect ratio, which is actually excellent for programming. If you did this on the new iMac, you'd get 2x 8:9, which is still pretty good. You soon don't want to miss the high number of vertical pixels.
What puts me off is the reflective finish. I can live with it on a 13" MacBook, but I'd find it impossible on that sort of size, where you're practically guaranteed to get a light source into view. Oh, and the fact that the HDD isn't user serviceable. Two hard drive bays would be nice, too, considering there's no eSATA or ExpressCard.
Interesting, how hard is it to apply without bubbles on such a huge screen? I think I need to see this somewhere in person before dropping any money on it. I've never seen this applied on any of the exhibit models in shops, so that could be tricky. Would you mind taking some photos from a couple angles and uploading them, google images isn't giving me joy? Thanks.
At my college job, my development machine had one vertical monitor for coding, a horizontal monitor for testing in the web browser, and another horizontal monitor for email, SQL server manager, or word processing. I miss that setup.
I flipped my monitor at work to 1200 x 1920. Excellent for almost everything, except working with some dusty old collaboration tool which has problems with flexibility.
I still miss 4:3. Much better for programming.