It does what it's supposed to do, but the process is a bit unintuitive -- you have to uncheck compatibility mode, recheck, reboot, then uncheck it again and reboot.
I haven't run across any apps that don't stretch, but I did notice that Zenonia is distorted in full screen, probably because Spare Parts stretches to fit and doesn't care about aspect ratio.
I also used it to run Droid Comic Viewer in full screen, but I ended up sticking with jjComics viewer, which doesn't need any stretch to fit assistance.