Since upgrading my iPhone 3GS to iOS 4.1, I've periodically seen 1 bar or "Searching..." at home and work where I used to have 4 or 5 bars. And I've sent text messages with 4 bars, only to have it immediately drop to 1 and the text message error out.
I'm trying to learn if I'm alone with this issue (and should therefore bring my phone to my local Apple Store—after trying a restore just so I can say I did when they inevitably suggest that), or if this is a common problem (and we should then file bugs at bugreport.apple.com).
Update (to answer Louis Gerbarg's question): I've installed every new update, so I believe I upgraded from 4.0.2 to 4.1. I think I noticed Apple's bar display calibration changes after the 4.0.1 upgrade, though the difference was subtle. I did not have dropped call problems and errors sending text messages until the 4.1 upgrade.
Update #2: I restored my iPhone to factory defaults (but still with 4.1 installed), and still had the problems. So I took it to my local Apple Genius Bar and explained this, and they exchanged the phone for a new one. The new iPhone 3GS had 4.0.2. But I still don't have the problems after installing 4.1. This must have been a hardware issue.