I sent 518.34 from MtGox to Dwolla on Friday (6 days ago) and got no confirmation.  I sent an email to info@mtgox.com yesterday and again today but no response.  I called Dwolla and they said positively there was no such transfer initiated from MtGox to my Dwolla ID.

MtGox needs a support line.  But at least they should reply to inquiries about a misplaced transfer!