Create a role that allows an org member to post to a blog.
This task has changed to an Outside Contributor role (see this comment: T734#14677). Submission-related aspects of this have moved to T864: Org member: submit for review.
User can't edit or delete other people's posts. User can't change blog settings. (user request, +1)
User can either publish directly to the blog or submit posts to an internal submission queue. Perhaps different roles: Author: can publish directly to blog - T738: Author role Contributor: can submit to internal submission queue