Garmins US Topo 100K maps are garbage. They are off by as much as 200 feet.
I know, I have the 550T with those maps, and it consistently shows me more than 200 feet from my actual position due to map error, as the unit itself reports the correct Lat Lon. Using topo maps I found here at GPSFD the unit is wonderful!
I called Garmin Support about this issue and was politely told that if I wanted better maps, I would have to purchase them, and the error in the 100K Topo was a known issue they were happy not to correct.
I have used the 100k topo product in various forms going back 7 or 8 years. There are indeed major errors regarding the roads. That is because they were based on Census Bureau TIGER data that wasn't originally intended for making into maps for GPS units. Over time, the quality of this data has improved, but there are still major errors. I make my own maps and have spent a lot of time with this data, correcting it by hand as needed.
Unfortunately, this is the most widely available and used form of road data for mapmakers on this site. You can't generalize, since the maps here were made by different people at different times, but in many cases you will find the exact same road errors on the free maps here because the come from the same source.
I would not call the Garmin 100k topo's "garbage".
Boyd, you are much kinder than I :)
The NW TOPO from GPSFD via Switchbacks is right on the money, while the Garmin 100K TOPO on my 550t is WAY off.
To illustrate, I will post images here soon showing the coordinates on screen with map placement, same GPSr, same location, only switching maps, to make my case.