Seth Godin's blog is among the Internet's most popular, and an obvious medium for promoting his books. But doing so overtly violates his own "permission marketing'' philosophy. For each of his recent books, though, he's deployed decidedly remarkable marketing methods. So in July, Godin launched a social networking site, Triiibes.com, a "gated'' online community of self-identified leaders, open only to those who preordered his new book. It opened to the public, by invitation-only from current members, last week.