Hi spike,
I recently had my HT300 installed with the latest 2.21 software. While it is difficult to find improvements in picture quality per sa, they have improved the user colour menu. Instead of the usual lumpy unresponsive RGB bars, they now adjust up or down, one unit at a time very precisely which gives much better control over the picture colour balance. For me, this really helps to get the best out of the HT300 without having to resort to the service menu. Well worth the upgrade in my opinion.
Best Wishes,
Paul H