This excerpt taken from the ATVI 10-Q filed Aug 8, 2008.
A substantial portion of Activision Blizzards revenues is expected to be derived from subscriptions paid by World of Warcraft subscribers. If these customers cancel their subscriptions, our financial condition may suffer.
A substantial portion of our revenues is generated by subscription fees paid by consumers who play World of Warcraft. Typically, World of Warcraft subscribers purchase one (1) to three (3) month memberships that are cancelable, without penalty, at the end of the membership period. If World of Warcraft subscribers become dissatisfied, they may chose not to renew their memberships in order to engage in other forms of entertainment (including competing MMOG offerings) and we may not be able to replace lost subscribers. Additionally, if general economic conditions decline, consumers may decrease their discretionary spending on entertainment items such as MMOG games and users may choose not to renew their World of Warcraft subscriptions. A decrease in the overall subscription base of World of Warcraft could substantially harm our operating results.