I've been using GeoBeagle on my G1 before I made my PN-40 my primary Geocaching GPS. The only times that GeoBeagle EVER had issues was when the GPS on my phone could not get an accurate fix. I know that it was not an issue with the application as Google Maps would also have the same error. Typically I would be placed within about 10ft of the location, and sometime right on top of it.
Now I usually use GeoBeagle for when I don't have any GC's preloaded into my GPS for the area I'm at.