The limits of GPS when navigating in close quarters are not about where you are but about where the chart makers thought they were when they charted the rocks. Illustrated with some electronic chart images.
For those not using the more accurate Differential GPS, here's evidence of the errors you will find using GPS for velocity and heading information when moving slowly.
For the novice, the very basics.
Forum for "expanding the use and understanding of Software and Utilities for GPS use." About 50 postings per month. A good place to get a question answered or just browse.
An e-mail discussion list about electronic aids. Over 150 subscribers.