Downloaded it and installed it a few hours ago -- here are my impressions:
- 3G signal strength is dramatically and noticably better. I used to maybe get a bar or 2 in my office and it's up to 5 bars.
- 3G voice calls are not dropping. Areas where I was dropping calls from the day I got the iPhone no longer drop.
- The 3G and Edge icons changed on the screen. I'm sure this is totally cosmetic, but I noticed it.
- The whole system seems snappier -- there've been times in the past weeks where the phone has been so bogged down that I can type an entire sentence on the keyboard and it takes 4-5 seconds for it to actually show up on the screen.