I've gotten lots of questions about whether the children (or husband!) in your household can use your digital kits. I've asked designers about this, and overwhelmingly the answer is yes! Sharing with your friends? Not so much.
kits are licensed to one user only: the person who purchsed it. Most designers have agreed in message board discussions on the topic that sharing is fine within a household for members of a household -- i.e. a mother buys a kit, her 12 year old daughter can use it. Having friends over to use the kits you bought is a shady area. My best friend digi-scraps and I don't let her use my kits, nor do I ask if I can use her kits. I personally wouldn't feel ok about it, since I know that it not what the designer intended when they sold us those kits.
Kits are not to be shared, except by family members in a household. One designer compared it to a gym membership -- you are the only one who can use your membership. You have to pay extra for a family membership if you want to bring people with you, and if it's a friend who wants one, they have to buy their own.
Hope that clears it up!