GoForChrome, I just met with the Garmin rep for the west coast a month or so ago and he said the new software will not be transferable frm one unit to another, up until now it has been so I guess its going to depend on whether you've got new software or some that has been sitting in a store for a while.
As for the Blue chart software, best cd rom Garmin makes, it gives you the same detail as a NOAA chart, excellent shore contour, depth readings, all nav aids, as well as all islands, not just the major ones.

Doug Kelly, I'm not sure which E-trex you have, I have never heard of a Mariner, as for the 76 & map76 the 76 is just a data unit (no map) the map76 has a world map built in and will hold 8 megs of download, $219 for the 76, $339 for the map76, I would highly recommend the map76. Best selling handheld on the market.