As Sony announced yesterday, Playstation Network has 20 million users. Xbox Live, by comparison, has 17 million But PSN is for the Playstation 3 and PSP (around 70 million devices), while XBL is only for the Xbox 360 (about 28 million). PSN has been around for 27 months. XBL? 67.
If you're interested in the business of video games, there's only one statistic of any significance: Sony has generated $180 million in gross revenue from PSN two-plus years of life. As of the last E3, after about five and a half years, Xbox Live had generated over $1 billion.