
It has been about 8 months since the release of OS 2.0, and 6 months since Apple missed their self-imposed deadline for push notifications for background applications.
This event is notable because it did not have a special event just for the iPhone 2.0 software when it launched last year.
The event invite gives no details beyond this being an "advanced preview" of what Apple is working on. But with an event, you can bet some big changes are coming.