My wife and I own Fascinates, I did the update on my phone not hers. This allows me a side by side comparison that does not rely on my memory. So should you update or not? The following information should help you make an informed decision if you are sitting on the fence.
First if you have a version of Froyo working perfectly well, you are out of warranty, no insurance and you are not tech savvy, DON'T DO IT, IT IS NOT WORTH IT. The difference between Froyo and Gingerbread is subtle not astounding.
Gingerbread does not look very different, all the visual differences are quite subtle.
Battery life with my phone was good before 2.3.5 and it remains good after, not better. reception has improved in my house from an average -104dBm (very bad) to -88dBm (acceptable). Gingerbread can be measured as faster with Quadrant Scores; before avearge was 990, after average is 1500.
I encountered problems with Navigation and Maps after update like many here and I believe they are corrected but only time will tell if correction is permanent.
In conclussion: am I happy with Gingerbread? yes with some reservations. Is my wife happy with Froyo? Very much so.
Are the differences between phones earth shaterring? No they are not. Good Luck with your decision.