At the top, there’s a tab that says “Tab this page”.
Click it.
Then click on “Design” in the main navigation below it.
See what happens?

Now browse around a bit and find a product that you like, “Tab this page”.
You now have a running tab interface inside of the site you’re using, thats being tracked by the site your using.

I haven’t bothered to make an account on the site yet, but I did close my browser, and reopen the page, and it kept my tabs. So its probably giving me a cookie of some kind to track that.

Ok, lets extrapolate how this could be useful.
Put this on a large scale ecommerce site that has you going between multiple views of products quickly, and needing to compare different things. Tabbed Browsing lets you do that, but its easy to lose your “state” in the ecommerce system if you forget to hit refresh when you go back to another tab in your browser.

Reference websites, where you may need to remember a location on something as you travel off a tangent to find more information on something else.

its a pretty slick interface trick, simple, but effective..