Assuming twitter_user is an instance of User and authenticated via OAuth,
opts = {}
opts['count'] = '200'
opts['since_id'] = twitter_user.since_id unless twitter_user.since_id.blank?
tweets = twitter_user.twitter.get('/statuses/friends_timeline', opts)
opts are not passed through, and tweets contains the last 20 tweets for this method, without regard for since_id
Looking through the dispatcher code, it would seem that this should be working, but I can't seem to reproduce.