Quote from FacebookGW2:
From 10th April, players can pre-purchase the Guild Wars 2 Collector's, Digital Deluxe or Standard Editions from buy.guildwars2.com or select retailers. All players that pre-purchase Guild Wars 2 will be given access to all upcoming beta events and will be given head start access prior to release. Follow the link for more information about this and our incredible Collector's Edition!
Access to all Guild Wars 2 Beta Weekend Events (sounds like the similar thing I've been doing with Tera every fortnight) ,Three days of headstart access