With Windows 7 it is easy to custom configure text settings to view on the big screen. I keep a text and internet
viewing settings enabled so it will go back and forth easily from gaming settings.

I am running a 40" HDTV. works great. How can you hook up three for simming? I have one Nvidia GTX 580. Can I do it with that. Will it work with DCS A-10C and Rise of Flight?

This may be a bit subjective depending on configurations. I've run even 1366x768 HDTVs as computer monitors and when the fonts are adjusted within the OS, they are exceptionally clean images. Properly configured, the text is easier to read on some HDTVs, in my experience.

The distance the user will be sitting from the display also plays a role. I know two people who use HDTVs full time for their PCs (non gamers). One guy sits barely 2 feet from his 32", and a lady who sits across the room from a bigger 40+".

My advice would be, since you are using HDMI you can't break anything. Just try it and see if you enjoy the results. Take a moment to experiment with OS font sizes and dot pitch settings. On a couple of occasions I got to set up my PC on 32" LCD and 42" and Plasma via HDMI and while the fonts were a touch larger on the desktop than I would prefer, once in game the graphics were spectacular by my tastes. And since I was running at less than the native resolution of my LCD PC monitor, I saw better performance as well. Quite an immersive experience IMO.

The guy sitting 2' away has low standards. A screen that size just isn't meant or built to be viewed at that kind of distance. Some people are ok as long as they have an image on the screen. Others want to get the most out of the monitor and will sit a proper distance from it. IMO, it's a waste of the equipment to sit that close. Like buying a Corvette but you never give it more than 1/4 throttle--yeah it's still fun, but you're missing out on what it's built for and has to offer.