FYI: Owners of 798, 997, and 1197 units should see a new S/W version in their accounts, that now has down imaging. Simular mode will have to do for a few months.
To everyones surprise, this also includes the older 797 which was previously said to not have enough memory for the DI mod. Even if you don't have a SI unit there have been a number of features added.
===================================from a HB rep:
This is the current list of all new updates as of 1/14/2010
New Releases as of 1/14/2010:
1197c - v4.750
1157c - v4.750
1155c - v4.750
DI uses data from Si, so your unit will not have DI. From memory, other changes included: Switchfire mode, more color palletes, support for Lake Master charts, faster GPS position updates, some waypoint management features, plus bug fixes.
I found the side imaging very useful but hard to read at first. This will be even better. I am now VERY happy that I the Hummingbird 797 over the Lowrance models.