Continental is now offering double elite qualifying miles as well (registration required).
Like the United and American offers, this one applies to travel through June 15. Unlike those offers, the terms and conditions do not require you to actually have purchased the ticket during the promo period. So it would appear that tickets purchased prior to today, but flown March 20 through June 15, will all count towards double elite qualifying miles. No need to cancel and re-book, eating applicable change fees!
So… who’s next?
(Thanks to D.R. for the pointer.)