My son was trained at barely 25 months. It only took 3 days of staying at home, with his pants off. That is the advice my mother had given me (she raised 5 of us!), so I followed it! For 3 days, I did no running around, and just stayed home. I kept his pants off completely, and moved a little potty with us from room to room. I asked him every 20-30 mins if he had to go. My mother said that they have to be able to feel the feeling, and see the result. He did great! That first day, he had a couple of little accidents, but figured out quickly what the sensation of having to go was, and he would go sit. We had read some books about it beforehand too. He learned fast. After the first day, he didn't have another pee pee accident (one poop one - but thankfully it was on the tile floor!). He had one accident in each new situation - meaning once I put underwear on him, he peed once in them before realizing that he needed to sit on the potty even if he was wearing pants. He had one accident out at a store, before realizing he had to ask me to go. That was it! I kept a diaper on him for naps/night - he usually chose those times to go poop. Eventually (6 mos or so?) he told me one night that he didn't need the diaper any more, and that was it. My daughter pretty much trained herself at 21 mos. My baby is now 19 mos, and she is already using the potty sometimes (I'm not quite ready to commit her to underwear, but I will once spring hits!).
My feeling is that you go with your child. My kids were easy, really, but I think it is because I stayed home & let them learn what it is all about. You can't be running a million different places and expect them to be comfortable with it. As someone else mentioned, give it a try, and if he doesn't take to it, stop, and try again a few months later.
I think that a 2 1/2 yr old or 3yr old is harder to train, because they have developed more stubborness. My kids never saw it as a battle with mom, it was just something they did. I also think it is harder for a child to learn it while at daycare/preschool, because there is so much else exciting going on!
Good luck! And don't worry - everyone learns to use the potty eventually :)
P.S. My son learned sitting down, and still sits probably 75% of the time (he's almost 6). My friend's son didn't learn quickly, however, until his grandma held him up to the toilet facing it - he preferred to stand!