They'll be distributing it with both Gnome 3 and a slightly-closer-to-ready version of Unity,
So, Unity will be able to display progress bars, notifications and little circles with numbers on the fly, like you might see in a Chromium-style plugin. I know, sounds small, but it's something. Third parties will also be able to write their own "lenses", which will let you search, for example, Youtube from your desktop -- IE, the search that happens when you hit the super button -- and browse interesting content from there.
They're going to integrate the Software Center with Unity a little more, not that I have any idea what that means.
I found those new features in these article: http://www.techdrivein.com/2011/05/6-important-changes-in-next-ubuntu-1110.html, http://www.junauza.com/2011/05/ubuntu-1110-oneiric-ocelot-features.html. But I'm sure there are a couple more features (mainly focusing on integration) in the works, as well as a nice pile of bug fixes. You'll also get Unity 2D, but I doubt you particularly care, unless you run a 5-year old 11 inch laptop.