Recently, news broke that Windows Marketplace for Mobile would allow you to share purchased applications with five other, separate devices. People, understandably, were pretty excited with this... though it almost seemed too good to be true. Well... it is. Microsoft has clarified how this actually works, and it's obviously not as first thought.
So what this means is that, yes, you can install your applications on up to five other devices, but you have to own them. You can't go giving applications to friends and family, and as you can understand, that is fair enough. Developers would be ever so titchy if they were theoretically losing out on four out of five potential sales. So, there you have it; this policy makes much more sense, especially from a profit point of view.