Apple's annual developer conference in San Francisco.
MacBook Shipments Have Begun?
The report cites "field checks" as the source of the information and describes the new MacBooks with a "very thin aluminum casing, an LED-backlit display and an aggressive entry-level price point."
This description matches many of the circulating rumors, including photos that claimed to depict the new MacBook. Also, the "aggressive" price point could also represent the lower margins that Apple predicted for future quarters during their Q3 2008 Financial Results. At that time, Apple described a "future product transition" which could impact margins.
The most recent claims have pinpointed October 14th as the possible day for the MacBook release.