I do stretch my monitors, I dont use windowed mode and when im a MP environment nothing changes, sure the UI is stretched but once I go to fly its all good.
Let me explain a few things, first I use an external progran to take my screen captures, and in multiplayer after I click fly everthing is good, I am away for the weekend and have no access to my machine so I cant take any SSs but I will be back monday, I feel if you cant run without being in a window you are not doing it right and am more than willing to help anyone set up there sim properly.
I honestly can say I am NOT an expert at what I am doing, but I have a very strong understanding of how my system works and how to get it to do what I want, that coupled with an understanding of how BSs file system works lets me see the results I want.