The PC Gaming Alliance have made their 2008 report to their members, and provided us with some snippets via the magic of a press release. The release claims that "The report provides an overview of the PC gaming market and the growth of the largest single platform for games with annual revenue of about $11 billion." The full thing is here.
The report also portrays "Massively Multiplayer Online Games (MMOGs) as the leading products for both revenue and profits. Other significant revenue generators include several Asian MMOGs making over $100 million in annual revenue after five-plus years on the market; World of Warcraft® producing over $1 billion in annual revenue; and the Lich King expansion to World of Warcraft outsold its predecessor. In 2008, two major subscription MMOGs (Age of Conan® and Warhammer™ Online) sold over 1 million units at retail."
I wish I had $11 billion. I'd buy a pony.