Update (Feb 22, 2013): Microsoft has clarified the transferability of Office 2013 and Office 365 installations in a recent blog post. In a nutshell, yes, an Office 2013 software licence is tied to the PC that it's installed on, and it's non-transferrable. The only exception is when the PC fails under warranty. If that happens, you can contact Microsoft support to activate Office 2013 on the replacement PC. However, there's no further word on what if the PC failed after its warranty period, and you were to buy a new one. Would Microsoft grant an exemption in this case too?
The image below shows how the previous Office 2010 and the new Office 2013 licences compare.
Source: Microsoft Office Blog.
Originally posted on Feb 15, 2013:
Eagle-eyed Office 2013 users have reported a change in the clause of the Software License Agreement (SLA) that states the installed application is non-transferable. It also implies the installed software is bound to its host forever.
With this updated SLA, it marks the amendment to two key parts of previous end-user license agreements (EULA) that came with earlier versions of the Office software suite. For example, in retail box versions of Office 2010, its EULA permits the user to install the software on up to two devices at once; usually a desktop and a laptop that are both owned by the user. Once the user retires one or both of his systems, the software's license is transferable to new machines.
This is no longer possible with the boxed retail versions of Office 2013 now and the site Office Watch has excerpted the relevant passages highlighted for attention. Users who think they can circumvent this by installing Office 2013 in a virtualized environment, its SLA considers a virtualized host as a physical one and requires a separate license.
Given the costs of owning Office 2013, it is very restrictive in terms of multiple usage of the software as well as the transfer of the license. In a nutshell, the SLA has downgraded the boxed retail versions of Office 2013 to the same status as OEM versions that are usually pre-installed on new PCs. For more information, do browse here for the online version of the SLA for Office 2013.