MuscleNerd, of the iPhone Dev Team, has announced a preliminary jailbreak for the iPhone 4S and iPad 2. According to MuscleNerd, it is a userland exploit that occurs after iBoot. Although the jailbreak has been successfully performed, he warns that it's too early to give an ETA for when it'll be ready for the public.

Here's what he had to say:
VERY preliminary 4S JB: (Huge missing pieces prevent public release. LOTS of work left)
Here is a video: