In 2006 we did heard of a program called as Flex Go which aimed pay-as-you go computing model but there was no real happening found but what I did heard today sounds very similar to the Flex Go model. Microsoft has added a new license program called as Rental Rights Licensing.
These are a simple way for organizations to get a waiver of these licensing restrictions through a one-time license transaction valid for the term of the underlying software license or life of the PC
So if you would like to rent out Windows to your customers you should have the Rental License for each computer. More details here.
The advantages as I see with the rental rights is reduction in the percentage of windows piracy. In countries like India where finding a genuine windows is very rare because of cost, Rental rights can bring a change. Imagine hundreds of Cyber cafes of which most of them run pirated versions. If they can get windows under rental rights they can not only enjoy the support of genuine windows but also get it cheaper.