Why do I have a dozen copies of certain preference file in my ~/Library/Preferences folder? I found the file .Globalpreferences.plist in my ~/Library/Preferences folder, but I also found the same file with seven characters appended to the .plist extension. 
For example: .GlobalPreferences.plist.jFulwSB.
In total there are 30 .Globalpreferences.plist files with appended characters.
I also found this behaviour with the com.apple.QuickTimePlayerX.plist file (192x), with the widget-com.apple.widget.stickies.plist file (106x) and the widget-com.apple.widget.weather.plist file (35x).

What are these files? Is it a backup? If so, what is backing them up?
Yes these are temporary file created by the NSUserDefault class when storing new preferences. 

First, the temp file is created, then filled with the data and then the temp file replace the older one and gets deleted. 

For some reason the were not deleted. You can check but I'm sure .Globalpreferences.plist has a more recent modification date than .GlobalPreferences.plist.jFulwSB. If it's in fact so, you can delete them.