Quick post - at the Ajax Experience conference, someone mentioned to me that IE was downloading background images multiple times if they were referenced in the stylesheets multiple times.  I checked with the team, and they confirmed that they did address this problem in IE7, and it should be fixed (they tried reproducing it multiple different ways to be sure).  Unfortunately, I forgot to get the name of the person who mentioned this to me - so if you're out there, this is fixed, and thanks for the feedback.