One more thing I realized - the sidebar currently shifts the page when expanded. If an expand-over-hover feature is added, then this behavior would likely need to be changed to float so it's not constantly changing the page layout when the user brows...
I love the implementation so far as a proof of concept. Would like to 2nd strxpdew's suggestion of having different shelves for containers. Maybe also an option to auto-hide/reveal the sidebars on mouseover? Also maybe a right-click option on New Tab...
