Anandtech has studied apple's new 4.01 OS update, and found that
the new formula for displaying bars covers a much greater
dynamic range. That is, it will show lower and higher signals
than before, assigning those more extreme values as 1 and 5
bars. This means it'll require more signal to show higher bars,
with the result of the iPhone showing 5 bars less often, but
also showing "no service" less often, too. [anandtech via
macrumors]