Helper function to determine if a user has blog posts already.
function _blog_post_exists($account) {
return (bool) db_select('node', 'n')
->fields('n', array(
'nid',
))
->condition('type', 'blog')
->condition('uid', $account->uid)
->condition('status', 1)
->range(0, 1)
->addTag('node_access')
->execute()
->fetchField();
}