Here's his problem:

  ->  Seq Scan on movie_person  (cost=0.00..10117.01 rows=97 width=8) 
       (actual time=2.540..59.933 rows=9 loops=1)
        Filter: (person_id = 160)

If he had an index on movie_person, that would be a ~ 1ms index lookup, not a table scan. You can't do that sort of database layout without putting indexes on the M2M mapping table.

(edit, oh, yeah, it's right there in the parent post....)