Interesting article from the Journal of Consumer Research.  In summary, when buying for multiple people gift-givers tend to be to distracted by trying to make the gifts to each different.  The better approach is to ensure they're buying the best gift for the recipient, even if it means some will be getting the same gift.

That's why gift-it is so great!  The options are the best for the person you're looking for, not random to ensure different items.

http://www.jcr-admin.org/files/pressreleases/121013065458_SteffelRelease.pdf