I think it makes it look much better than when I had the standard SD receiver.
The reason why is the HDMI all digital connection (or the 3 cable method for those that done have that connector on there TV- cant remember the name).
Both look great.
I still putthe HD Tivo in 480i mode and let the big screen take care of the wide mode stuff as that is what looks the best.
I put the HD Tivo in 1080i mode only when watch HD channels.
The SD channels all look DVD quality once you tweak your TV settings to the new receiver (a required step).