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 tweetedthat 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.
I wish they were thicker, like the mod (original) version. That way, when they're extended and used as platforms they actually look like solid objects. Now, if you block a water flow or player movement or items dropping, we'll have more things-being-stopped-by-solid-nothingness which Minecraft has plenty of already. I like the stone/wood look. But I like the old shape. I also agree that they look flimsy.But, still, YAY PISTONS! (or whatever they're called)
I think they changed the design for two reasons:1. This looks more fantasy2. This looks a lot easier to get the materials to craft it (6 gold/iron and 1 redstone is hard for ME to get (actually, just gold -- I have 100 iron on my SSP save), but wood and stone/cobblestone are a lot easier to get)