However I've been amazed with the battery life post the repair and upgrade. I didn't return the battery to the Samsung service center so I know they didn't slip me a new battery.
Admittedly I've been pretty light usage since the upgrade but still. Here's a series of screen shots taken each night when I plug it in for the night.
The lowest reading during those seven days was 67% remaining.
I personally don't think that Gingerbread is responsible for the majority of the improvement. I think that the factory reset and the resulting clean-up had the biggest impact.