"Katie got heaps and heaps of invitations. Some were engraved ecru paper, some were digitally printed, some were plexiglass prisms with orchids inside," says Alexa. "But all of these very fancy forms of invites were really formalities, because even the bat mitzvah invitations were followed up by emails or scanned versions of the invitation."

Since its launch in the fall, Paperless Post has sent more than 60,000 invitations for over 1,000 events. (Full disclosure, the Hirschfelds are friends of mine.) A recent benefit for Elie Wiesel's foundation, featuring Natalie Portman as a guest of honor, used the service, as did an event Zac Posen hosted for Ballet Hispanico and one some Diane Von Furstenberg staffers threw to support the Mirwais School Fund. Right now the service is open to members only (membership is free, though a user must receive a Paperless Post invitation). "We want it to grow organically through people who actually know each other," explains Alexa.

Members can send up to 12 invites for no charge each month. For bigger fetes, users must purchase a virtual "stamp" per invite. (A pack of 60 stamps costs $5.)