Just got an email through from Game, offering £15 in voucher code if you preorder before the end of Feb, however....
You have to spend the 3x £5 vouchers before April, you have to spend over 20 quid to use them and you can only use one per transaction. Oh and the vouchers can turn up in March!
You can't use the vouchers on preorders either.
So potentially you'll be buying 6 full price games before April and saving a whopping £15.
You might be able to work out a fiddle, preorder games that come out at the end of the year, use the vouchers, then cancel the preorders. However as most stuff is soooo overpriced you'd be much better off with Shopto.