I have been using Safari 4 Beta the last day, and it is SMOKIN! So quick (Here are some stats to back up my experience). "Top Sites" is brilliant. This is potentially a "Can't live without" feature in the making. Cover flow makes searching site history a dream. I am going to give it until March 8th to see if it will overthrow Firefox's reign on my web-browsing. Definite potential.
Beyond Safari, there is some exciting things tid-bits that have been revealed about Snow Leopard. The "put back" option for files that have been trashed seems like a given. I have gone to my trash wishing I could restore a file back to its original location on multiple occasions.
Apple has continually tweaked Stacks. On its first interpretation it seemed more gimmicky then functional. But by adding the ability to view as list, and now with the upcoming ability to graphically drill down into folders (as shown in the following video), Stacks is showing promise.