Schema:

Comment:
  tableName: comment
  actAs:
    Timestampable:
  columns:
    id:
      type: integer(4)
      primary: true
      notnull: true
      autoincrement: true
    comment:
      type: string(500)
    user_id:
      type: integer(4)
    story_id:
      type: integer(4)
    video_id:
      type: integer(4)
  relations:
    User:
      local: user_id
      foreign: id
      foreignAlias: Comments
      class: sfGuardUser
      onDelete: cascade
      onUpdate: cascade
    Story:
      local: story_id
      foreign: id
      foreignAlias: StoryComments
      onDelete: cascade
      onUpdate: cascade
    Video:
      local: video_id
      foreign: id
      foreignAlias: VideoComments
      onDelete: cascade
      onUpdate: cascade

SfGuardUserProfile:
  tableName: sf_guard_user_profile
  columns:
    id:
      type: integer(4)
      primary: true
      notnull: true
      autoincrement: true
    first_name:
      type: string(64)
    last_name:
      type: string(64)
    user_id:
      type: integer(4)
    company:
      type: string(64)
    profile_text:
      type: clob(65535)
    picture:
      type: string(64)
  relations:
    User:
      local: user_id
      class: sfGuardUser
      foreign: id
      foreignAlias: Profile
      onDelete: cascade
      onUpdate: cascade
      foreignType: one
  options:
    type: InnoDB

sfGuardUser:
  actAs: [Timestampable]
  columns:
    id:
      type: integer(4)
      primary: true
      autoincrement: true
    username:
      type: string(128)
      notnull: true
      unique: true
    algorithm:
      type: string(128)
      default: sha1
      notnull: true
    salt: string(128)
    password: string(128)
    is_active:
      type: boolean
      default: 1
    is_super_admin:
      type: boolean
      default: false
    last_login:
      type: timestamp
  indexes:
    is_active_idx:
      fields: [is_active]
  relations:
    groups:
      class: sfGuardGroup
      local: user_id
      foreign: group_id
      refClass: sfGuardUserGroup
      foreignAlias: Users
    permissions:
      class: sfGuardPermission
      local: user_id
      foreign: permission_id
      refClass: sfGuardUserPermission
      foreignAlias: Users



Query:
    return $this->createQuery('sc')
            ->leftJoin('sc.User u')
            ->leftJoin('u.Profile p')
            ->where('sc.video_id = ?',$id)
            ->orderBy('sc.created_at DESC')
            ->useResultCache(true,sfConfig::get('app_story_comment_cache'),'comment_'.$id.'_'.$page);

Html:
  <?php foreach($pager->getResults() as $comment): ?>
    <li><?php echo $comment->getUser()->getProfile()->getDisplayName();?> said at <?php echo $comment->getCreatedAt();?> -
        <?php echo $comment->getComment();?>
    </li>
  <?php endforeach;?>

Results in 4 queries(one for each of the getProfile()->getDisplayName()

If you drop off the useResultCache it results in one query, the very first one.