I tried this on my 3GS at different places. Some places, the bars dropped from 5 --> 0. Others it went from 5 --> 3. In some other places, it didn't drop at all. It's pretty random, but the effect is certainly repeatable at the same location.

I noticed just now that my iOS 4.0.0 3G was at 4 bars. Lifting it slightly, I got up to 5. Holding the base, sandwiched between both hands, I managed to push it down to 2 bars (you have to wait for a bit, there seems to be a delay of five to twenty seconds between each step).

However, I have to wonder at this PR, changing the discussion from whether it is unusual to dropbars from how the phone is held, from whether it is unusually easy to miss-hold the iPhone 4.

Ditto.