I agree with villas - *but* check for those renegade queries in your models. once upon a time i tried loading config options and other data in db.py so they would be globally available as lookups without querying the DB each time. it worked like a champ, until i got lots of data, then it was horrible.
so my guess is that there is something in your models takes a long time to execute as the amount of data increases. good luck! christian