insert vs select into performance

Hi

I was doing some testing on "insert" compared to "select into". I
inserted 100 000 rows (with 8 column values) into a table, which took 14
seconds, compared to a select into, which took 0.8 seconds.
(fyi, the inserts where batched, autocommit was turned off and it all
happend on the local machine)

Now I am wondering why the select into is that much faster?
Does the select into translate into a specially optimised function in c
that can cut corners which a insert can not do (e.g. lazy copying), or
is it some other reason?

The reason I am asking is that select into shows that a number of rows
can be inserted into a table quite a lot faster than one would think was
possible with ordinary sql. If that is the case, it means that if I
write an pl-pgsql insert function in C instead of sql, then I can have
my db perform order of magnitude faster.

Any comments?

regards

thomas