I know your wife, our kids are around the same age. We're in the middle of potty training too.
Monthly thing: After 2yrs, you go by halves: 2, 2.5, 3, 3.5...
I read somewhere that kids have this weird hangup: "Also, a lot of children think they have 'lost' part of their body when they make a poop and worry that their insides are going to come out and then disappear down the toilet! Saying a ceremonial 'goodbye poop' before flushing helps children overcome this anxiety."
I can believe having your kids trained fairly early. I taught Pux Jr. the sign language sign for milk when she was pretty young and the "toilet" sign is pretty simple to do, it's just getting to know your kids really well. Plus, my kids would always make this one particular face when she was trying to pinch a loaf, so I could sometimes get her to a toilet and I think this might have helped with her being comfortable around the toilet. (and if you remember a particular picture I posted in the poop vs. puke thread, you can understand my aversion to cleaning diapers Edit:link for the curious
http://forum.calgarypuck.com/showpos...4&postcount=87 )
Does he have a sit down potty that is his size or are you using a seat on your bathroom toilet? We had her own down stairs and did the "run around naked" thing and let her sit and watch tv while doing the deed (although the new problem is when she sits on the potty, she's there for 15 minute, even for just a simple #1). Have you tried putting a potty behind the couch as well?
I think it's just persistence. Don't cave and put diapers back on, or you'll never gain any ground.
Good luck!