What's new in 4.0 may depend also on if you have deployed any add on modules. If not, feel free to point out that there are new pay layouts that were upgraded from 3.0 to 4.0 which allow more options for look at feel of the personalized homepage. Also, you'll find more widget available.
We added categories to 4.0 for spaces and groups to easily organize content ever better, an enhanced activity stream that shows summaries of that content as well as addition actions such as status updates, and finally we have private discussions and documents that can be tied to user's profiles instead of having to live in a content container.
Hope this helps.
Thanks, Billy. I pretty much have what you outlined below from the "What's New" doc Jive provided.