I recently bought some knitpicks circs so I could try 2 circ socks (not sure about doing both at the same time, though) and decided to get 16" and 24" in 1, 2, and 3, in addition to the 32" I already had in them. I read that it's easier to tell the needles apart when you use two different lengths. After reading all your opinions, maybe I'll try 24" and 32" as well as 16" and 24"..
By the way, I LOVE my knitpicks. It's hard to go wrong with them!