Google's effort with its Chromebooks is laudable but anyone that has ventured into buying one such device knows the experience is not yet complete. That does not mean things won't change in time. Android tablets are selling like hot bread these days. But many realise the devices don't reach their expectations.
Like a smartphone a tablet's main advantage is its mobility. Now depending on the model and screen size the device is good for playing games, watching movies, browsing and more. As far as productivity goes - here these devices are not there yet. Even with a keyboard and mouse attached the experience is not the same as a PC/Laptop.
It's not about the OS. You can get a tablet running Windows 8 - Microsoft Surface/2 that also comes with an attachable keyboard but that device is as close as you can get for average productivity. A laptop is still a far more versatile device and can help you get things done a lot faster. Not to mention the fact that the Windows OS offers far more complex apps than Android in terms of productivity and more.
Bottom line - get a tablet for entertainment, communication, gaming and browsing but not for true productivity. For that the PC is still the king though I expect not for long.