Temp tables performance question

I have a question about performance issues related to temporary tables.

IIRC temporary tables were implemented as ordinary tables with some 
pre/post-processing to give them unique names so that they would not 
clash with similar-named tables from other sessions. 

Is this all that is done or has some work been done to improve their 
performance further?

I'm mainly interested in INSERT performance as this is the area that is 
much slower than other operations.

IMHO temporary tables could be made significantly faster than "ordinary" 
as they are only accessed inside one session and thus have no need for 
locking or even WAL as they could do with max 2 copies of the same row 
the other of which can be discarded at end of transaction thereby making 
it possible to provide much faster insert behaviour.

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Hannu