I received a few email today regarding AirAsia X launch. From what i gather, booking is now available until 30 November 2008 for flight from 11 March 2009. I'm not sure how true this date is but i guess you can check the website for further information. Now, the best part, price for a one way journey from Kuala Lumpur to London(STN) is £41 without tax and £99 with tax(according to an email i receive). I even did a simple check on the website as shown in image.
This is just a random check, which shows a total of £127 for a return ticket from London(STN) to Kuala Lumpur LCCT(KUL). Although this price is excluding tax, it is still very cheap comparing to currently available flight. I think the cheapest before is Qatar, Brunei or Emirates at around £400- £600 including tax.