RAM-only temporary tables

An idea for a possible enhancement to PostgreSQL: allow creation of a
temporary table without generating any disk I/O.  (Creating and
dropping a three-column temporary table within a database transaction
currently generates about 150 disk writes).
If some circumstances don't make it feasible to always do this as a
RAM-only operation, perhaps a clause could be added to the CREATE
TEMPORARY TABLE syntax to specify this behavior along with whatever
limitations on the temporary table are required for this to work. 
(For example, maybe this is only feasible if the table will be dropped
by the end of the transaction?)
-Kevin