Office for Home cannot be used in a Business
the Terms and Conditions are clear, and with the upcoming release of Office 13 that will surely have a free upgrade path buying a PC in the next month or so some businesses may delay pc purchase
Volume Licensing with Software Assurance will grant the upgrade right for businesses.
I recommend a quick read to the following blog
Home and Business edition has no limit of users but cannot enjoy Volume Licensing rights for imaging for example.
Be careful with what you buy