blueranger: I had put up quite a few foam panels on the back-wall, and at the first reflection points on the ceiling and side-walls. I felt things sounded too dead, so I removed some, and noticed an improvement in dynamic impact and a wider soundstage. Also, I tried covering my 60" plasma set with a thick comforter, and didn't feel there was any improvement.
In short, I guess there is not much point to an omni-style speaker if you're room is treated so that all the indirect-radiating sound is absorbed and not reflected. And remember; these speakers are voiced with the reflected, indirect-radiating sound taken into account.
I want very badly to try some diffusers instead of absorbers to the sides and behind the speakers. Sadly, diffusers are a bit pricier than absorbers. But I may try some ebay specials if they aren't too heavy (I suck at things like mounting heavy objects on my drywall-over-stud walls).