This is nice!
One small problem: the active “hit” area doesn’t quite match the tab when it’s expanded.
So when I hover over a tab, that tab slides open, but then the mouse isn’t over an active area, causing the tab to slide closed… which triggers the tab again.
Tweaking the active area of an exposed tab should correct it — otherwise, this looks great.
One request for a new tab would be a “MailChimp Subscribe” option.