Are you running full-screen or windowed?
If you're regularly task-switching to take screenshots and stuff, it's easier to run the game in a window.
Full-screen. My concern wasn't so much my own issues with it, but the possible issues players may have with it. Personally, I take my screenshots with Fraps, but they could want to task switch for any number of reasons.
Obviously I could tell them to just not minimize, or to hit another key after maximizing to fix Escape not working. I don't think I've experienced the hyperspeed thing GarageGothic has though. It always goes the proper speed.
But, perhaps it is a combination of a Vista thing and one of the updates to the engine. I run Vista, as does the tester.
It sucks because I can't really help you identify the problem much beyond that. The best I can say is, if you'd like a reproduction, create a game, make a GUI that becomes visible upon pressing Escape. It should work, until you minimize/maximize the game again, then it will stop working until you feed it a different key press. Clicking with the mouse however doesn't seem to re-enable the Escape key. Only keyboard presses.