It might be me, I could be getting senile or something but I just noticed what I think is a new feature that does not seem to show up in the list of 200+ new features. It is one of those little things and this one although quiet is actually really cool. After pushing Aperture 3 and putting a lot of new features through their paces to discover depth (I love Aperture's depth - there is always more than meets the eye), I stumbled onto "sticky selections"
It seems that Aperture three retains image selections individually for every single browser view for every single object. Project, album, smart album, everything. If you make a selection and click somewhere else on the library and go back your selection is still exactly what it was before. You can make a selection in one project, jump to another album in another project, make a new selection, etc, etc. Every single one of them will still be there when you go back.
What's more is that these selections are all persistent even if you exit Aperture and get back in. Very very handy. I actually noticed this when stress testing the heck out of the new project/library merge features and I have a lot of good news on that front. I think I will write up some of my findings today or tomorrow. Just one or two other things that crossed my mind to finish figuring out.