For people who attended PAX or the Eurogamer Expo and had the chance to try out CS:GO also received a Beta Key. People are desperately trying to get their hands on them online with some people paying up to £40 pounds for them on eBay. It was recently suggested (by Chet) that people do not buy these keys online as there will be an open beta in October.
I would also like to encourage people not to purchase these keys online as many scammers are using this desperation to their advantage by selling fake Keys to the innocent Counter Strike fans. I would not worry about missing out on the beta as Valve know what people want and will not leave anybody out.