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They way I sort things, I really like iPhoto 08's "events." Basically it assumes that pictures taken close together are from one event and auto sorts them that way. You can also sort using albums and such just like the older versions.

I haven't played with it that much yet.
 
If I remember some of the upgrades I really liked:

Improved searching.
Events organisation and the little gimmick whereby you can roll the pointer over an event and quickly scroll through the images therein.
I believe the fullscreen editing mode allowed more pictures than the older version.
Truly non-destructive editing.
Better editing tools (highlight/shadow editing - although they're not that good)
Copy/paste edits (so you can apply the same edits to other images).
 
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