I'd seen this one a couple of weeks back, it certainly looks interesting but there are drawbacks...
As eric says, low capacity - a decent NiMH AA cell is around 2800mAh, these are only 1300mAh.
Secondly, verrrrrry slow charge - 5 hours to achieve half the power of a "normal" rechargeable?
Thirdly, lack of USB ports! I already have a 4 way hub AND a 7 way hub hanging off the back of my iMac and they're both fully populated!
Fourthly, a battery charger isn't exactly costly (cheaper than some USB hubs!) is much, much faster and will charge several batteries at a time.
Fifth, look at the cost
High-street stores are still ripping people off (at least in the UK) for standard rechargeable batteries, I always end up buying from 7dayshop.com as their rates make sense... these cost 6.50GBP each as opposed to, say, Panasonic 2600mAh for 1.87GBP each from 7dayshop. The difference on 2 batteries would buy a cheapy charger!
Nice idea, can't see it working as a large-scale commercial proposition, although the niche market of wireless mice / keyboards / games controllers may find it handy...