Obvious way to subsidise
The obvious way to subsidise the cost of the hardware would be to have a banner ad at the bottom of every page served. That's a LOT of ad impressions, even if people only use it for half an hour a day.
Hopefully Google don't go down the path of getting the very cheapest possible components, I'd like to see some real quality in the hardware.
To really capture the market's attention they'd need some amazing new piece of technology and useability - I don't want to see a simple rebranding of some other manufacturer's netbook.