There's been some interesting data released by The NPD Group that show information on the current top 5 MMO/PC Game Subscribers.
"Now that NPD can estimate the value of the subscription market, it's clear that there is a sizable chunk of revenue being generated by PC gaming beyond what is reflected in retail sales," said NPD analyst Anita Frazier.
PC retail sales declined slightly from just over $1 billion in the US in 2006 to $910.7 million in 2007. This did not include digital distribution and online subscription sales.
NPD said there are 11 million gaming subscribers monthly.
The billion-dollar figure includes three categories: MMO, casual and console revenues. The firm calculated the figures by taking the online revenue average of Q4 2007 ($94.3 million) and Q1 2008 ($80.1 million), in turn taking the average of those figures and multiplying by 12 months.