I found this in a magazine help DVD. I can't cut & paste it so will have to type it manually. It refers to the maximum number of folders Windows can handle. You can exceed this number, but then you will start getting problems with settings not being remembered.
Start Registry Editor and navigate to: HKEY_CURRENT_USER\Software\Microsoft\Windows\Shell. Create a new Dword BagMRU Size with a value of 1,000.
Then repeat the procedure in:
HKEY_CURRENT_USER\Software\Microsoft\Windows\ShellNoRoam.
Exit and re-boot for the changes to take effect. You can increase the number to any value you want, the standard default is 400.
Hope this helps.
TFP.