Cydia is completely functional.
The jailbreak is completely functional.
The untethered portion is still up in the air, though, given the 4S uses the A5 like the iPad 2, one could presume that the devs could already have an untethered iOS 5 JB for the iPad2/4S (as well as older devices obviously).
I'm crossing my fingers for an untethered JB by the 10/21/11, but I think that's very unrealistic!