Hi!
I came to this topic following a link in the "German forum".
My HCx had 2.60/2.60 when I bought it about 6 months ago. Since then I've twice been hiking in a canyon and I've twice had the offset-problem: drifting away from the path in the topo map up to 50 meters constant offset until re-powering the unit. In addition the unit froze three times logging a track in the map view. I had to press and hold the power button, the display faded and then the unit worked again. So I was happy to read the changes made in SW 2.70.
Now as I decided to update from 2.60 to 2.70 Garmin released SW 2.80 yesterday. So I downloaded eTrexVistaHCx_280.exe from perry and also downloaded the zip-file with the 2.50 GPS SW from the German forum. First I updated to SW 2.80 (GPS SW still was 2.60 after that), then I copied the 2.50 rgn-file in the folder where the updater.exe was located an dragged&dropped the rgn on the updater.exe.
I'm looking forward to making experiences with 2.80/2.50!
By the way: do I have to make a hard reset?
Greetings
Manfred