I was looking around for it, but I found it, finally! Under Windows 7 Pro, it's here:
C:\Users\<username>\AppData\Roaming\Macromedia\Flash Player\#SharedObjects\<random string of letters and numbers>\localhost\Program Files\VVVVVV\VVVVVV.exe
With the <username> and <random string of letters and numbers> being unique to your installation. To clarify, "VVVVVV.exe" is a folder which holds a bunch of ".sol" files, which I assume are the vital files.