Dynamic Side-Tabs

The "My eBay" area of eBay uses a system of dynamic side-tabs for navigation to child (subordinate) pages. Here are the tabs in the normal state:

Here is the "Saved Stuff" tab in the rollover state:

Once you click on a tab it stays open; closing the previously-active tab:

I think this is an interesting approach to help de-clutter a left navigation bar, which can sometimes  contain an overwhelming number of links. The key, however, would be clear groupings of links—with labels that convey a strong "information scent" of the underlying links.