If we crot Twitter account of MuscleNerd (one of the Dev Team members), the first firmware update for iPhone OS 3.0 would be imminent and it could also be already downloadable on iTunes as of this Tuesday.
This update is relatively expected because it should correct some problems of youth of iPhone OS 3.0, such as battery and Wi-Fi management.
We do not know yet what will be the exact name of this update (3.1 or 3.0.1?) But in any case, do not make this update if you wish to keep your jailbreak and especially if your iPhone 3G / 3S comes from abroad. Indeed, the unofficial unlocking will no longer be active during the update!
This information remains however to take the tweezers but it is certain that Apple should not traner to offer this update anymore.
We prepare on the forum.
(Thank you Bidier for the info)