Pretty much any programming shop you know will have dual screen monitors for their developers. There are a bunch of posts and studies about the potential productivity gains. I have been running dual 20" monitors at various jobs for a number of years. I have a 21" monitor and a 17" at home.
Generally when gaming at home I don't use the second monitor but maybe I need to get some work done but I want to monitor a football game. I can leave it running via a web page on the second screen or I will have the browser there with Java Doc for my current coding project. They gave away some older 17" LCD monitors at work so I grabbed a couple of them a few months back. I hooked one up to my wife's laptop and she can't believe how usable it has become. She does a lot of Excel / Word / Browser work.
I gave one to each of my sons. The one in high school uses his to keep the homework assignment up while working in Word. Much easier to keep track of all the requirements for the paper when you don't have to toggle between windows.
My other son has his hooked up to his laptop in mirrored mode. This allows his tutor to monitor what he is doing without hovering over his shoulder. All of them getting plenty of use and in a variety of methods.
Great, you love dual monitors but what is the deal with bigger ones? Generally bigger is better, up to a point at least and that is also the case for monitors. Just going bigger without the up in resolution would not have mattered. We needed some monitors for our medical coding department. We figured we could give them our existing monitors and we could get the upgrade. Just like it works at home where my old machines filter down to family members when I upgrade.
None of us wanted to lose vertical resolution. We were running 1600x1200. If you go 23" you end up losing vertical as most are 1080 for that dimension. Once you get used to see X number of lines of code you don't want to give it up. Almost all monitors are widescreen now. The new ones are 1920x1200. Bonus extra width, same height in pixels. My boss is thinking of just using one as they are so wide. I am running dual and loving it. The extra width means I was willing to split PSPad and Chrome on one screen and Eclipse and Explorer++ and other apps on the other. I can still see the same amount to code but I don't have to toggle between windows.
I keep all my random thoughts on program ideas, to do list, etc. in various tabs of PSPad. I copy things from the web into there and into Eclipse all the time. Now I feel I have the screen space to keep everything on screen and open. That is a productivity gain.
The new monitors also have better color making my graphics artist work easier too. Newer tech, not the newest as these are still the value line Dell monitors but better than the old ones for sure.
If you develop and you don't have dual monitors you are really missing out. If you do have dual monitors and have been running 20" for a long time then at step up to 24" may well be worth your time.