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 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.