I have the same issue in that the skysports hd football ls not as crisp and clear as last season, a couple of my football mates have also said the same and has been mentioned quite a lot on these boards, but not seen any answers!
I don't have any issues with other sports on sky, in fact the F1 is a perfect picture! I think sky have done something to how they are transmitting the football this season. There are quite a few similar comments, but no answers, other than it must be user set up, but I don't believe that's the case. I have a few friends that all say the same!