Delete Cascade FK speed issue

Hi,
I've dbase with about 80 relations.
On deleting a user, this cascades through all the tables.
This is very slow, for 20 users it takes 4 hours, with exclusive
access to the dbase.
No other users connected to the dbase.

Ok I know there will be somewhere a relation with a FK without
index, which
is being scanned sequentially. But how can I find out what postgres
is doing
while it is handling the transaction?

Is there a way I can find out what postgres does, and where it hangs
around, so I know
where the FK might not be indexed. (The dbase is to big to analyze
it by hand).

The way I do it now is to check the pg_locks relation, but this is
not very representative.

Is there profiling method for triggers/constraints, or a method
which gives me a hint
why it is taking so long?

thanks in advance