Update: Keith pointed out in the comments that Picasa Web added this feature awhile ago. Thanks for the tip, Keith.
I too often brood over whether to make my Flickr photos public or private. If I make photos public, I risk random creeps ogling pictures of my wife or even worse my kid. If I make the photos private, I force non-net savvy family members to sign up for a Flickr account, which they probably won't do, which means they'll never see the photos.
According to Lifehacker, I don't have to trade privacy for convenience anymore. Flickr has added the ability to share private sets via email, and they don't require the recipient to sign up!