I have been seeing a few people talk about this issue while I have seen plenty of others saying that they have had no problems at all. My wife and I both have Droid 1s and are having no issues at all with the 3g. I really wish I could tell you how to fix it. I have seen others say that they have put the phone into airplane mode and then back out and this has brought the 3g back. I have heard people saying that completely wiping and reflashing the rom has worked as well. I wish you luck in figuring it out though and sorry that I can't help ya out any better than this.
In my research and troubleshooting I've found that there seem to be two things that cause me to lose my GPS signal for no apparent reason. The phone becoming too warm (battery temp over 42c, and a large Google Maps tile cache... usually 16MB or bigger.
While simply cooling off the phone and clearing the map tile cache from Google Maps individually don't seem to fix the problem, doing BOTH seems to help considerably. My recommendation for Droid X users who use Google Navigation with background music and perhaps a car dock application is to 1) clear your Google Maps map tile cache, and 2) mount the Droid by the A/C vent. This combination seems to work well... but on longer trips you might want to clear that cache at rest stops.
Best of luck on the roads, Android road warriors! Remember to use your Bluetooth headset and keep your eyes where they belong... on the road!
The problem I have been getting is the gps is not getting my exact location correct. When I am driving in the city, the gps sometimes puts me on a parallel street to the actual street i am on. It is usually off by about a block or so.
The quality of a GPS fix is based on the numberof satellites that your handset can see. A basic fix can be obtained from as few as 4 satellites, but the more satellites that are visible, the more accurate your position will be!
Consider downloading the free app GPS Essentials to help troubleshoot GPS signal quality. I've been using this app for a while and have found it quite valuable!