The widely reported hack (which actually originated in the forums) that allowed users to get on iOS 5 beta 1 without being a registered iOS developer or having a registered UDID has been fixed. This comes by way of forum member s0init, who reports that the hack has been plugged:
Confirmed: Bypass activation has been fixed. Sorry folks.
Another day, another hole fixed, it seems. We’ll update as we hear more, though it is safe to use iOS 5 beta 1 until August 4th. After that, it seems, the software will expire and it will render your device useless until you restore.