Nintendo is not the only sponsor of PAX. The lengthy list includes game developers, hardware manufacturers, and industry media outlets. Microsoft is another big name at the event-- The Expo’s keynote “The Prehistory of Xbox” will be delivered by former MS employee Alex St. John.
PAX 2005 had around 9000 attendees. According to the PAX ’06 website, that number will increase for this year. Those in attendance have access to the event's huge exhibition hall, industry-related conferences, live music concerts, and gaming tournaments. PAX ’06 takes place August 25-27.
Source: Penny Arcade Expo