The mail server that processes all email from moodle.org was taken offline by a freak explosion at our ISP:
http://tech.slashdot.org/tech/08/06/01/1715247.shtml
As a result all email from this site (copies of forum postings and messages, as well as signup emails) was lost for a period of 36 hours or so.
Everything should be OK now, but if you're waiting for a signup email you might want to try signing up again. Please contact us via support@moodle.org if you continue seeing problems here.