Its actually not that messy when they are 2. Its when they start using the molds and cutters, and small tiny piece of playdoh fall onto your carpet - that is when the mess begins

Moon Dough is EVIL. It looks so fun but try it once and you'll see what I mean. It fractures into a zillion pieces and is a b-tch to clean up. DH has banned it from our house.

I think we introduced it closer to 1 year, and it was always fine. As a PP said, DD had obviously been told "don't eat that" in school. We also have a little table that's supposed to be for art, but the reality is that the play-doh tends to travel, especially because she likes to serve us meals made out of it in various places (breakfast in bed, etc.) It's not that hard to get out of anything, though we have hardwood floors, so maybe carpet would be trickier.

2 is a good age. That is when my son started using it at preschool. One of his first sentances was "It's play-doh. it's not food. no eating." clearly he learned that at daycare.

We have a little kids' table in the dining room that we bring into the kitchen for anything messy - playdough, paint, chalkboard. Then we just wipe down the tile afterward.

DS got playdough for his second birthday, and it's worked out great.

For messes, we just bought a Kiddy Platter from some parent inventors who also have friends who invented an edible craft dough (it's called "Yummy Dough"). How's that for a great combo! Just do a google search for it.