yeah ive just treated my room and its dampened the top end flutter down a lot.. now i can listen to my mix for longer before my ears tire out and im not getting a false impression of the top end (which tended to make my mixes sound a tad muddy).. i did use proper scoustic tiles though - but its well worth it :)
as baz said a foot or two of dense foam in the corners could well tighten up the bass response of the room.