I2C - Distance Limitations / Slave to Slave

what is the longest distance you can run an I2C BUS wire before you ran into trouble? will using twisted cables help?

in my case i am looking to wire about 4-6 Arduinos over about 12m (36ft). There are some beefy 10A DC motors in the proximity but i can route the signal wires as far away as possible.

Another quick question since I am very new to I2C: can slaves talk to slaves? or just master-slave1, master-slave2...etc. ..since its a bus i hope that slaves can communicate but I never tried nor found a source.

thanks - phil

Check out - http://www.gammon.com.au/forum/?id=10896 - it is one of the most complete I2C arduino stories on the net.