I am not having any problems with 3G reception in the Northern VA area. However, AT&T has problems with 3G converge, despite their 3G viewer map showing total coverage in all metropolitan areas.
Apple changed the iPhone 3G display code in v2.1 to "properly represent the signal strength". This means they rewrote the display code to show more bars for the same signal strength as before on the iPhone. There has been some blogsphere that the code change was to align the display of bars with competing carrier displays. Who knows! However, I am getting about -30dB in my home in the burbs which is excellent signal strength. If you're getting about -100dB you should be seeing about 1-2 bars and obviously receive less signal strength and increase the chance for dropped calls or slow data transfers.
There is a keypad entry you could use to display the dB signal strength on your iPhone. See
http://discussions.apple.com/thread.jspa?messageID=8095609�/
I'm convinced Apple is working to finish getting the bugs out of the iPhone. Give them some time. High technology and the Wall Street pressure for ROI forces many high-technology companies to get things out the door quickly. Consider Windows, and the darkside still haven't gotten is right yet!