My Son Will Not Actually USE the Potty!!!

Sounds like you're getting frustrated, and I can completely understand! My oldest was 3 1/2 when he finally learned, and it was a frustrating process for us, mostly I think because I didn't know what to do to help him.

Generally, it sounds like you're doing everything right. He's showing the signs of being ready to learn and is learning to recognize the signals from his body. It sounds like you have a "potty chair"; we tried that and then switched to the big potty. For some reason, he preferred it, and it was one less thing in our small bathroom. But either way is just fine. You might want to check out the book I eventually used, which was "Toilet Training Without Tears." It has lots of great advice on the entire process, and one of the things that helped up most was an Elimination Chart. I noted the times of wet and dirty diapers, potty "tries," and using the toilet. It helped us to see his pattern and get him there at the right times, and he really loved getting to put stickers on the chart (at first every time he tried, then we switched to every time he went on the potty, and finally for a few weeks it was a sticker for every day with no accidents).

We had a similar problem, with getting off the potty and immediately peeing. And I've seen it with other kids too (I do day care and am potty training several kids all the time, it seems). With my son, books helped, since they seemed to take his mind off what he was doing so he could relax a little. Another little girl I know actually used to sit and sing a song: "Re-lax. Let the potty out." She would sing very slowly with deep breaths to "let the potty out." It seemed to help her a lot to avoid the tensing up when she sat down.

Finally, if you want to try it, the thing that really did it for us was a few days of "bare butt." After my frustration with treating pull-ups like diapers and cleaning what seemed like hundreds of pairs of underpants, I finally undressed him from the waist down (but it was summer, so it might be less practical now). I had to keep a very close eye on him, of course, but as soon as that potty started to come, we would race to the bathroom. At first, there was a lot of cleaning up messes, but it only took a week or two to see a marked difference. And I didn't worry about poop accidents, especially since the Elimination Chart helped to know when to get him in there anyway.

I hope some of that helped. This can be very frustrating, I know, and you're not alone. Good luck!

The Cheerio target idea is a great one!
With my older when we thought he was ready I sat him on the potty every 30 minutes for an entire day. We bought him Thomas underwear that he picked especially for potty training and told him that he had to pee and poop in the potty so Thomas would stay clean. Since he loves Thomas it worked really well and we didn't have a single accident. Later, after the novelty wore off he had a couple accidents so we told him that when Thomas gets dirty we have to throw him away. That got him "back on track".
Since you have a baby on the way you can tell him that because he's such a big boy now he can use the potty and let the baby have the diapers. If he feels like it's a privilege to pass them on he might be less willing to soil them.
Last idea: I babysat a little girl who knew everything your son does and still used her diaper instead of the potty. One day, while changing as especially potent diaper I told her, "This is disgusting! Do you smell the stinky? Do you like the stinky on you?" Of course, she said no so I continued, "I don't like changing stinky diapers and I don't want to do it anymore. It's gross! You're a big girl now and you need to put the stinkies in the potty, not in your diaper. No more pooping in diapers!" I know it sounds mean but the next day her mom said, "I don't know what you told her but she only wants to wear panties and has been using the potty all day."
Good luck! I've got a little over a year before I have to potty-train my little guy and I'm not looking forward to it. =)

Try putting Cheerios in the toilet and tell him to pee or poop on them- use them as a 'target' (even if he is sitting to go potty)
I know they sell 'potty targets' somewhere, but Cheerios work just as well.
For some reason that worked for my oldest son.
however, my 2 1/2 yr. old refuses as well. "do you need to go poopy?" 'No...' "Are you sure?" SHakes head No.
swear to you, less than a minute or 2 later he reaks...
"Did you go poopy?" 'No'... "You're gonna get a sore butt... Did you poop?" still respond, 'no'!!!!!
I haven't been trying too hard yet, but, man, you'd think after having a sore butt after us not discovering a poop for awhile would give you a little incentive to try the toilet anyway.
Good luck to ya.

When I was potty training my son he would not sit on the potty chair. Instead he took the cup from the chair and would pee in that but would never poop in it. He also would want to use the big potty so I just let him and he was happy and started going to the bathroom all the time. I have a 2 yr old daughter right now that I am trying to potty train and I decided to skip the the potty chair and bought her one of those cushion seats for the regular toilet so she won't fall in. She loves sitting on it and feeling like a big girl so now we are working on her being able to know when she has to go. Good luck!