From the looks of things, the iPhone 4 jailbreak and unlock is stable and working on the iPhone 4. It is still suspected that the dev team are waiting for Apple to release 4.0.1 before making their jailbreak public. We chatted with Wang this morning about the unlock, and he mentioned Apple's definitely catting this mouse (or is it the other way around?):
Apple has thrown in a few extra tricks targeted specifically at previous unlocks (including blacksn0w and ultrasn0w) in order to mitigate the damage we can do (i.e. unlocking the phone) even if we found a bug. But we got around it. :P
We'll be keeping you updated as the situation progresses!
UPDATE: Another recent tweet, this time from @MuscleNerd sheds more light on the unlock progress:
MuscleNerd: We think we have 3 different ways to unlock once inside BB (the 3rd way was first to fully work for @planetbeing !)