I'm running 6.0.472.0 and I notice this now and then. I download a file, and I get a duplicate extension. IOW if the download should be "download.zip" it saves the file as "download.zip.zip" likewise if it's an exe setup file instead of "ProgramSetup.exe" I get "ProgramSetup.exe.exe" and in the status bar where it asks if you want to open the file it shows the double extension. It's not just in Windows explorer.

Kind of annoying as I have to keep renaming files just to kill off the extraneous extensions.

I'm not using any kind of download AddOn... just the Chrome built in.
It seems to go away for awhile, then it will start up again for no apparent cause.

btw it does it on both Windows Seven 32 bit and Vista64 SP1.