I think that a feature permitting users to share menus and grocery shopping lists with selected individuals online could be very useful.
Suppose the wife usually does the grocery shopping and cooking, but something pops up unexpectedly when the fridge at home is empty, and she can't go to the store or be home in time to cook that night. The husband could then access her grocery list and menu, and of course he would have access to all of her recipes! (Assuming he wouldn't just order a pizza...but I think you can see where the ability to share these features with certain other users would be useful in any number of circumstances.)
Of course, password protection would be a good idea.