Well this isn't a case of not enough signal strength since I was getting speed and direction, but twice the speed and a difference of about 45 degrees in heading. Besides, I have sailed this area for years, my GPS didn't change, and I didn't hear about any satellite problem.I look for sensitivity, antenna type (can you use an external antenna?) and such... You can also - if you are of a mind - find a cheap (but good) USB to GPS interface for a PC.
--jr
I have thought about adding a "hockey puck" GPS to my laptop and using that for backup. There is one listed at ebay that looks decent for the price of less then $40.