I assumed we were allowed to put it on at least one other computer for personal use, but didn't know it couldn't be on two portable ones. News to me!
Most retail versions of Office allow a single user to install a second copy on a laptop, tablet computer or other portable machine. The second installation is intended to be used by the primary user while travelling, at home or at a satellite office. The terms of the licence make it clear that only the primary user can run the software, and Office itself enforces that requirement. If a second user opens an Office product on your portable machine, it connects to the Internet to check if another licensed copy is running. (This catches out users of pirated product keys) (The EULA says "BY USING THE SOFTWARE, YOU CONSENT TO THE TRANSMISSION OF THIS INFORMATION." in capital letters) If it detects the license code is in use, the application will politely inform the second user and quit. Legitimate use on two machines simultaneously (comparing two versions of a spreadsheet, for example) isn't prohibited by the license, though you will need to turn off network connections on the second computer.
The exception among retail editions is for software marked “Home and Student” edition, where you may install one copy of the software on up to three licensed devices in your household for use by people for whom that is their primary residence.
According to the Microsoft Office EULA, which you can download from the Microsoft Software License Terms (MSLT) for Microsoft Office 2010 page, you can clearly read that you can legally install single-pack Microsoft Office on two computers.
The same applies to earlier versions of Office.
According to sub section c "Portable Device", of section 2 "Instalation and Use Rights": "You may install another copy of the software on a portable device for use by the single primary user of the licensed device”
This was confirmed by a reply tweet on Twitter by Microsoft Australia.
This applies to all Microsoft Office products. Word, Excel, PowerPoint, OneNote, Outlook, Outlook Social Connector, Publisher , Access, InfoPath, SharePoint Workspace, Project Standard, Visio Premium, Visio Professional, Project Professional, and the Home and Student versions of the following: Excel, OneNote, PowerPoint, Word.
There are however a few caveats:
You have to have bought a legal copy of Microsoft Office, and be the legal user of the license.
You have to be the only user of the license.
You can install Microsoft Office on a desktop and a portable device such as a laptop or notepad. The license terms do not seem to allow you to install on two desktops or two laptops for example.
Both computers, desktop and portable, need to be owned by you. In other words, you cannot install Microsoft office on your laptop and on your friends or families desktop.
The license only applies to Microsoft retail products and not OEM products.
http://www.microsoft.com/About/Legal/EN/US/IntellectualProperty/UseTerms/Default.aspxMaybe now you can see another reason why people turn to open source alternatives?