I have decent signals (Wi-Fi or 3G) where I live, but I find that on certain apps that use the internet (Safari, Facebook, Mail, etc.) the connection will freeze entirely even if I switch between the two.
Also, my iPhone 4 keeps kicking me off 3G onto EDGE randomly. Sometimes it will kick me off data altogether and then display "No Service" and "3G" in the top bar.
This never happened in any other iOS 4 release on my phone and worked perfectly fine under iOS 4.2.
Otherwise, my battery level has not been affected too much by the update. If I can think of any difference, it would be that I end the day with around 33% of battery left compared to the usual 43%.