There's only two downsides I can see to sharing your account with your hubby.
- He'll really know how much you're spending on ebooks!
- Unless your tastes are in sync, he'll probably give you grief about all the [romance / vampires / whatever] books you like!
Also, if one of you gives the other a gift card, Sony's default is to always debit the gift card rather than give you an option to purchase the book and leave your gift card credit untouched. So he might use up your gift card balance without knowing!