I use Sprint Nav all the time. Never had a problem with it, ...seems to work flawlessly for me.
I like it better than my Garmin Nuvi! ;-)
I've been using it w/ my rooted nookcolor (Froyo), tethered to my Pre w/ freetether - I load up GoogleMaps on the nook to follow along, and the 7 inch display is so nice - i hardly ever look at the Pre, anymore. ;-)