John Beaver <john.e.beaver@gmail.com> writes:
  

Ok, here's the explain analyze result. Again, this is Postgres 8.3.3 and 
I vacuumed-analyzed both tables directly after they were created.
    

 Merge Join  (cost=1399203593.41..6702491234.74 rows=352770803726 
width=22) (actual time=6370194.467..22991303.434 rows=15610535128 loops=1)
    

                                                        ^^^^^^^^^^^

Weren't you saying that only 50 rows should be returned?  I'm thinking
the real problem here is pilot error: you missed out a needed join
condition or something.  SQL will happily execute underconstrained
queries ...

			regards, tom lane