Where is the cookies folder under Windows 7/8 ?

To view the cookies folders under Windows 7/8, you need to modify the Windows Explorer behavior to show "protected OS files" first:

Open Windows Explorer (Windows + E keys)
Navigate to: Explorer > Organize > Folder and search Options > View > uncheck "Hide protected OS files" and apply the setting.

To view the cookies folders once you can view hidden/protected files, you can simply navigate to:

Windows 7
C:\Users\username\AppData\Roaming\Microsoft\Windows\Cookies
C:\Users\username\AppData\Roaming\Microsoft\Windows\Cookies\Low

Windows 8
C:\Users\username\AppData\Local\Microsoft\Windows\INetCookies


Notes:
You can also reach the cookies folder fast by copying/pasting the following in your Explorer address bar:
%appdata%/Microsoft/Windows/Cookies

With IE Protected Mode turned on, the browser runs as a low privilege process, and it stores cookies in the LOW version of the cookies folder:
%appdata%\Microsoft\Windows\Cookies\Low