DRJAD
I know this is anecdotal evidence but I would avoid any GPS whose design is very old, say 10 years, and most of the cheap Garmin models are that old, or close.
While many people have told dark tales of GPS errors of many miles, and certain magazines are always delighted to publish these, nobody has to my knowledge ever come up with more than 2nd or 3rd hand accounts. But where one questions these people, they either don't offer any further information, or they own up to the GPS being some very old product. It would not suprise me if units developed in the early days did have firmware bugs, and the market leaders in this game run their old designs for as long as they can.
boomerangben
I won't get into this age-old debate except to say ...
To fly into the ground you've got to be too low relative to the ground!
In VMC this is done by losing control of the plane (not a navigation issue).
In IMC you need accurate navigation to be able to remain above the MSA. A GPS is by far the most accurate and the most reliable and the least error-prone nav device available to man. Anyone half smart will use it in conjunction with other means, and the "primary/backup" designations which the anti-GPS brigate is so fond of are inapplicable.
But in any conditions, flying by looking for hedges, railways, motorways, etc, and getting the GPS out of the bag only when you are lost and have just flown overhead a big airport with two parallel runways (but with no apparent traffic except a load of 747s at the holding points) is not the time to do it. You get the full benefit only if you use it in conjunction with visual navigation, throughout the flight.
And you shouldn't be entering waypoints. Always go for a moving map model. Anything less is a waste of time and money because you WILL get lost with it.