That was maybe not one of the most exciting keynotes Steve has given, mainly because he's talked about almost all of it before.
Stacks was new to the keynote but a patent showed up on that years ago. It is really great to see it come up. Though to be honest about it I've been doing something similar for ages, I put Home, Applications, and a few other folders in the dock to accomplish the same thing.
The Core Animation stuff looks wonderful. I presume he was using a maxed out Mac Pro, I wonder if that cool animated video search tool is going to be available or was just a developer plaything. I also wonder if a MacBook could handle all that video playing at once.
A lot of developers are bummed over not getting a real SDK for the iPhone. In all likelihood one will be forthcoming in time but not now.
Going cross platform with Safari is pretty interesting. I am going to be thinking about that a bit more.
That huge picture of the Library of Congress was great. You could almost read the titles on the books when he zoomed in all the way. And that the title he added was smooth all the way in was awesome.
I am still curious about the other 290 features that are coming to Leopard will be. Actually Apple's website lists a whole bunch though I didn't count them. I am really impressed by the new voice they have, that will be nice.