I would agree with the last response. My son is 3 yrs old and was just potty-trained this past August. We too used pull-ups, but he wasn't "getting it." A friend of ours suggested just going straight to underwear. I had done that before, but I hated the messes and constant laundering of clothes. But that's what finally did it for him. We did it...went straight to underwear. I made sure there were about 3 days straight that I didn't have anything else to do so we could work solely on potty-training. We did use pull-ups at night for a little while, just until we saw that he was consistently waking up dry.
Also, with the underwear, I would make sure he went to the bathroom about every 20 minutes at first. If he didn't go then, I'd make it 10 minutes, then 5 minutes... until he went on the potty. I also kept a chart with stickers. That was not only helpful for HIM as he LOVES stickers, but it was also helpful for me to be able to see the pattern more clearly so we wouldn't be going to the bathroom every 10-20 minutes.
Just keep working at it. Some kids aren't ready when you think they are...or ought to be. We didn't think our son would EVER get it.