Alt-Left Arrow and Alt-Right Arrow currently navigate backward and forward through the history of items opened. sort of. A more logical response to these commands is to cycle left and right through the tabs currently opened.
The current response to Alt-Left Arrow doesn't always go back to the last item viewed if you closed it, but sometimes it does. The navigation is unpredictable and unintuitive.
For those of us who prefer the faster operations of a keyboard than a mouse, this is a big deal.
Oh yeah, and make it work in all three clients, not just the Notes client.
A related issue is Ctrl-tab: