For an accurate test of your 3G signal strength, and to see if the 2.1 update really does someting, other than just bump the bars up visually, put your iPhone into "Field Test Mode" prior to the update and then after the update. Example:
To do so, go to the number pad and type *3001#12345#* hit send.
Look at the numeic indicator next to your carrier logo in the upper left of the screen. The lower the number, the weaker the signal. Keep in mind that all numbers are actually - negative. The closer to 0 the better the signal. This is resulted from the carrier, not from Apple.
-75 gives all 5 bars of strength. Call quality is perfect.
-105 no bars, just barely hanging on to 3G. Call quality is sub par.
to exit field test mode, just hit your home button. Ther are a slew of other things in this mode that you can see, but unless you are a UMTS technician, most of it will be gibberish to you. This will really tell you what is going on behind the scenes of the signal bar.