Same problem here. I downloaded WP 1.5 less than a week ago (after 2005-04-15) and my situation is:
– outgoing pingback (auto) does NOT work (tested with different WP and MT blogs)
– outgoing trackback (manual) does work
– incoming pingback and trackback both work
Since pingback is supposed to work fully automated, I can’t tell if my WP even *tried* to do the pingbacks, or, if it didn’t due to some config errors.