(*  small apple script to save rating into grouping field and
   vice versa. Perfect to persitent store your rating witin the file
*)

tell application "iTunes"
	repeat with stars from 1 to 5
		set rating_value to stars * 20
		set group_name to "" & stars & " Stars"

		set sel to (every track whose rating is rating_value and grouping is "")
		repeat with aTrack in sel
			tell aTrack
				set grouping to group_name
			end tell
		end repeat

		set sel to (every track whose rating is 0 and grouping is group_name)
		repeat with aTrack in sel
			tell aTrack
				set rating to rating_value
			end tell
		end repeat
	end repeat
end tell

Btw. for each Star rating I do have a smart playlist which allows me to find those quickly.