Dan Frommer, writing for SplatF:
1. The number of announcements at the event. Perhaps: iOS 6, new iPhone, some big new Apple iOS app, new dock connector, some hardware accessories?
2. The number of colors the new iPhone will ship in.
3. The number of inches in the new iPhone’s display, vs. the rumored 4-inch screen.
He goes one to list seven more items that the blatant ’5′ shadow could mean. Some seem more likely than others, but all are possible.