management of pg-schemas: pg_temp_n and pg_toast_n ?

This is occurring In an 8.4.2 pg database, and I have noticed it in 8.3.10 as well.

We do a lot of work with temp tables here, and over time a lot of pg_temp_[n] schemas have appeared.

Similarly, we notice build-up of pg_toast_[n] schemas.

Is it ok to drop these if they contain no tables?

Or is there a way to prevent them from persisting past a given life-time??

Mr