I have a Garmin 541s that I bought in March 2010 and agree with many of the post here. There are times when it is spot on and there are times when it's not even close. Less the latter though and the problem is clearly that the charts are inaccurate.
Not really sure how to keep this device and its built-in charts up-to-date as there appears to be no mechanism to do this from Garmin.
Really do not like Garmin's Home Port application and prefer MacENC and the NOAA charts instead.
The most interesting use of the Garmin is it's track feature that I have used to follow a previous pass through an area. In the end, I really don't understand how to use all the features of the Garmin or it's just really limited for functions of storing and maintaing tracks.
I tried using Home Port to plan a trip and found that Active Captain and other online resources were much more valuable.
Garmin's MapSource program works well for me but I'm using Garmin's Blue Chart that I have on CD's. I'm not sure and I have not tried to upload from a unit any charts/maps preloaded onto that unit for use with MapSource. Is that what the Home Port program is used for as distinguished from Garmins MapSource?