I think it's a great idea..
I don't understand why people are so upset about this. It seems like a fantastic idea.
Imagine having a work set of tabs, a home set of tabs and then sets for everything else as shown, shopping for example, or news articles that you havn't got round to reading yet.
For all those of you that say why not open two instances of the browser, what happens when you close them both? What set of tabs does it keep? Why have two instances using up (already copious amounts) of memory when you can solidify it into one neat tidy package. Which you can then sync to your laptop in a matter of seconds, when you want to go into the living room to watch a bit of tv and do some relaxed browsing.