I changed my pre-order from Gameplay to Play.com... i figured that i was better off saving the £8 and risking not getting it on release day was more prudent than spending that extra money on guaranteeing it on the 28th.
EDIT - i changed back after reviewing the 3-5 working days thing with Play... i pre-order something in order to receive it on the day, not the week after. Man am i picky. =)