I did a lot of reading after Christmas and decided I want to go with the 765T which includes the lifetime FM traffic.
I believe the 785T has 9 months of MSN subscription for traffic and a few other web based "services". After that you pay an ongoing fee to keep the MSN stuff working. I you want the MSN features, this is the way to go. Or, if you do not want the traffic warnings at all, get this unit and let the MSN subscription lapse.
I think all the other features are the same for a 765T and 785T.
There is a compariosn of the different models at the bottom of the linked page.
If you see a new (not refurb) 765T for 2 bills, I am ready to pull the trigger.