While Notch, Carl, and Daniel are all off at E3, Jens and the others have stayed behind to continue work on Minecraft. Jeb has just tweeted that pistons are working in single player, as well as in SMP, however the latter looks glitchy.
He also mentioned that they will not be called pistons, but what they will be called has not been determined yet, either.
Another reveal, is that there are plans for two types of pistons, one that is normal, and another is sticky. The sticky one presumably can stick to the block it pushes, and pull it back after it is deactivated.