My only add-on is that most THX products are actually better built than non-THX products, but that is not directly related to the THX certification, but more to the fact that THX certification falls on the more expensive product lines, so you should be getting a better quality product anyway.
Now, I have a Pioneer Elite receiver that is THX certified, but I didn't care about the THX certification. I wanted to features, build quality, and price combination that it gave me. The THX certification really didn't play into the purchase.
As already mentioned, you will hear from others that the certification itself generally doesn't mean anything, and I would agree.
When I was in the market for a receiver about 16 months ago, I was told that as long as you are in the $500+ price range, you will get a very nice receiver. Now, market prices have gone down for models that have been around a little while, so that number may be lower today.
