I might actually buy one of those - I've always wondered why I can't pair with multiple devices, I'm assuming that switching between them is like using a KVM switch and the other connections are not dropped between switches.
However I wish they included a touchpad on the keyboard because even my tablet likes to have touchpad input.
Recharging via USB... Awesome! (edit cause I'm an idiot)
I have a wifi keyboard for my WD TV Hub.... and my Asus Infinity has a docking keyboard and can control my WD Hub, and my laptop... and my phone is a worthless POS... so I don't really have much need for any such device right now.... I can certainly see how others would though!
I can only truly work on Logitech gaming keyboards. I used one for 7 years (G15 older model), so when it broke my world got flipped upside down. I bought a G510 which I am largely satisfied with. Although I see the usefulness of a keyboard like this, I still hate wireless keyboards/mice because of batteries. If it had some sort of charging dock you could leave the keyboard on while not in use, that'd be great.
If it had a trackpad, it would be great for a HTPC setup. I bought a mini keyboard and trackpad for my HTPC several months ago. It works pretty good but occasionally I would like to pair it to my phone for text messages without having to disconnect it from the computer.