Safari restores the buffered state of videos when you undo a closed tab →
I often close tabs by inadvertence and wish I did not hit ⌘+W so quickly. Fortunately, as you would undo anything in any text editor, ⌘+Z works in Safari and re-open the tab you just closed. Even the buffered state of videos will be restored now with Lion.
Pretty handy and one of the reason why Safari has my preference.