Apple Seeds iPhone 3.0 Gold Master to Developers With WARNING

Apple has seeded the iPhone OS 3.0 Gold Master to developers but warns it will lock your iPhone into "testing" mode.

This version of iPhone OS 3.0 should only be deployed on devices dedicated for iPhone OS 3.0 GM Seed software development. By installing iPhone OS 3.0 GM Seed software
on your Authorized Test Devices, these Devices are permanently “locked” into testing mode and cannot be restored to an earlier release of iPhone OS. Bear this in mind before installing the software.

Although we have not had a chance to investigate this deeply we would strongly suggest that normal users DO NOT install the GM seed which is bound to spread across the internet soon.