Buying from the App Store at work
When you buy an app on the Mac App Store, you’re getting the rights to
  run that program on any Macs you own and operate, for your personal
  use. Basically, if your household has a half-dozen different Macs,
  including desktops and laptops, you can buy a copy of Gratuitous Space
  Battles and play it on every single one of them. Consider a purchase
  of consumer software via the Mac App Store to be a bit like buying a
  household site license for the app.
  
  The situation is slightly different for apps that are considered
  commercial or professional in nature. For apps that fall into this
  category—Aperture’s a good example—the Mac App Store license says that
  you essentially can install that item on computers you use or on a
  single computer shared by multiple people. Basically think of it as a
  one-seat license for a pro app.
  
  In other words, the Mac App Store’s purchasing system is not designed
  so that a podcasting company can spend $15 for GarageBand and equip 30
  different Macs with a copy. But if you want to buy a game and put it
  on your desktop Mac, your laptop, your wife’s laptop, and your
  daughter’s laptop, go for it.


Find the full article here :
http://www.macworld.com/article/157018/2011/01/appstore_licensing.html