And to be clear I have Vista 64 with UAC turned off.
This quick and easy solution will save you the hassle and after applying this fix you can quick save/autosave as normal and steam
can't diddle with your files.
You need Administrator rights for this and I'm assuming that most of you do.
Go to the steam userdata subfolder and look for a folder named remote that has the quicksave files which steam insists on backing up.
Right click on the folder and go to properties, then under the security tab look through the list till you see your name, select it
and in the permissions list below it either remove you deny yourself ALL permissions.
Hit apply and close out all the windows and try to access the folder you changed. You know you did it right if you get
a window saying something like "You currently don't have permission to access this folder."
If you can't access it, neither can steam.
Now you should be able to play the game and quicksave/autosave all you want and not have to worry about it again.
I've tested this and it works like a charm.
If you are worried about locking yourself out of folder, create another admin account and undo the above changes.
Sorry if this isn't clearer but I'm really tired.