With all the problems noted with Express and downloading maps in general, I thought I would post of my good fortune.
I've been putting off updating the maps on my Zumo 660 and iMac for along time because of all the reported problems. A few days ago I bit the bullet and jumped in using Express. No problems with the download to both devices.
Turned of the energy saver features on the iMac and in less than 2 hours the 660 was updated. In 15 minutes the iMac was updated. I did individual downloads.
I think the latest iteration of Express works, at least for me. I'm glad I procrastinated long enough for Gamin to work out the bugs.
Leading up to this I posed a lot of question on this and other forums about updating. I would like to thank all that replied.
Len