First of all, I read all your responses and I'm surprised at how a couple of the mom's are acting like it's terrible that you haven't potty trained him yet. You are NOT way behind schedule so don't stress!
I have a five year son old that was potty trained by 22 months. He was just easy... my husband was off work for a week and in that week he trained him, no big deal BUT he is still in pullups at night because either his bladder is small or he sleeps too sound. (We've asked the pediatrician about it and she says he's not old enough to really worry about it).
Now..... I have a 2 1/2 year old son that I TRIED to potty train as early as we did the first one and it so did not work! He is a different kid. Unfortunately I didn't figure that out until about a month after I had tried everything possible and stressed myself out completely. I decided to finally stop trying because we were moving in with my parents and a month later moving into our own house. Now that we are in our new house for a month he has just now started wanting to go potty every time his big brother goes so we are about to lose the diapers (except for nights) and start Potty training boot camp!
I hope this helps...don't get discouraged, all kids are different and will train on their own time. OH! One more thing, my pedi says that with some children, it is completely a battle of wills. You know how willful two year olds are anyway, they can avoid pottying when over stressed about it just because it's not their idea!