I don't see most IT shops doing anything other than supplementing their PC fleets with devices. If an organization decides to go further, it might be to buy x86 tablets and docking stations. Where I work, all of the office workers are now on large dual monitor setups and none of them would care to go to anything less.
Also, keep in mind that a PC is a device. Devices and services is just a way of saying that if you provide a strong set of services, they can be accessed through any device. In the case of a service like Office 365, you get a solid back-end service with local software for either desktop or mobile devices.
I think an important step in all of this will be the ability to plug Azure roles into your 365 instance for custom applications. It might be possible now, but as an easily configurable supported scenario it would be killer. I know a few small business who will be all over that.