email is not sufficient identifying information. email addresses change more frequently than do given names and surnames. the entire point of usernames is to abstract identity away from such volatile attributes as email address. a profile's unique identifier should remain static even when any of the profile's attributes change.
Regarding using email as an account identifier and having Cosmo send out invitations to share: Supplying another person's email address to a service, even an ostensibly benign one, without their permission is a breach of confidence. I know someone who goes ballistic when she receives an email "invitation" to share my photos, calendar, etc. from a third-party service. She fears her email address will wind up on spam lists. So the issue here is not just having your calendar spammed, but having someone receive unsolicited email from a server they don't know. A "ticket" from a personal contact that gives the intended R or RW access avoids having a causal sharee (perhaps this scenario could be limited to Read Only) having to provide either their email or set up an account. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Open Source Applications Foundation "Design" mailing list http://lists.osafoundation.org/mailman/listinfo/design
