Yesterday we spent the day out on the beach, so he got to run around with no diaper or pull up on, he was concerned with pee'ing, but I quickly made it known that pee'ing in the river was completely acceptable. After that, he came up to me each and every time he went pee.. "Mommy, I pee'd in the river!!!!!!" He was so super excited. lol
Today we spent a lot of the day with no pull up on, just big boy under-roo's (yes, he actually calls them under roo's), and he did SOOOOOOO well. Up until the point he went behind my chair, hid under a blanket and craped his pants.
I by no means scold him for pooping his pants, not even when he does it in his underpants. I do try and encourage him to mess in the potty, and try to tell him why we need to poop in the potty.
I think taking him to the potty every couple of hours will be a very good start, also with the cheerios. We did do that at one point, but got kind of lax on it, so we'll pick that up again.