I love this upgrade, it depends much more on sidebars now tho... Sidebars are apples worst invention ever... If you like to view your apps fullscreen they're hidden, you wont even notice they're there. Some Apps shrink the main window when you fold out a sidebar, but still, it's terrible interface design, why show important options that are part of an app somewhere hanging alongside that app?
Being able to use column file-view now is an insanely important new feature, thanks! But (there's always a but) using Apples way of column-viewing it takes up so much space, and invokes scrolling in 2 directions! Whats wrong with the unix/MS way? Just as a nice tree of just folders, with their contents viewed on the right?
Also, this app needs to be more keyboard-control friendly. There's no way to get out of the sidebar without using your mouse for instance... One more thing: I just LOVE the preview functions!