I've been testing various games (800x600 and 1024x768) at various monitor resolutions up to 1680x1050 with maintain aspect ratio checked and unchecked. Everything worked as expected. That's the good news.
The bad news is that I ran into some other problems when I kept the test version of WME installed and started working on copies of my projects. Over time going in and out of the game in Debug mode, I ran into several problems. I'll report them, but don't know how helpful it will be since trying to reproduce these is going to be tough.
1) After pressing Esc to display menu, lost mouse pointer and had to end game in task manager. (This happened twice, and had never happened to me before with WME.)
2) Several times game froze and had to end using task manager. Rebooted, restarted project manager and was able to run same game fine without changes, so it seems to be some kind of memory leak? (This happened 3-4 times, and had never happened to me before with WME.)
3) Huge slow down. It got so that it took four or five minutes to start a small game. (I've had some problems with this before, but never to this extent. In the past I always thought it was DirectX related since this computer - a Dell E1505 Dual Core with ATI Mobility Radeon X1400-- has problems I attribute to Dell's non-existant graphic card driver updates.)
I hope this is the kind of feedback you wanted. If I can nail things down any better, I'll let you know.