NEW CMS - What goes and what stays?
In terms of the content management system portion - everything stays, content, pages, images, snippets etc - so upgrading will not cause any issues with your sites pages or content whatsoever.
Featured listings: Featured listings will need to be re-uploaded. The featured listings manager has gone through a complete overhaul to the point where it is a completely different system (WAY BETTER!) and there is really not a way to move the information over, as much more information is required for the new system to create a listing.
Leads: All of your leads will be moved over, so no issues there - your leads saved favorites and saved searches can also be moved over. What cannot be moved over however is the "tracked visits" - Visitor tracking is done in a completely different way and upgrading to a new tracking system means the tracked visits will not be coming along for the ride (Very few users even looked at this in the old system anyways)
Drip email: With the invent of the document management system, the way drip email campaigns are handled has completely changed - Drip email campaigns will need to be re-created using the new system.
Starting LEC 7 soon but it won't be called LEC 7 - LEC 2012 coming soon!