Rando,
I have also had mixed results with dry ice however, if you keep the esky in the shade, cover it, wrap the ice in newspaper and only acces it once a day, it seems to last ok. We use it for our 'holding' esky' and access it only every second day to remove two days of meat (another hint is to get your meat cryovaced in useable lots). We then place this in the normal eskys and work from there. We have kept meat frozen for up to 8 days using this method on an 8 day block. I guess it comes down to protecting the dry ice. Regular use of the esky is not the way to go!
Ross