My 3yr old was completely potty trained before I took him with me to take care of my grandmother in another state for two months. It threw him for a loop and he regressed for a while. I let him, until we had been home for three months and I realized that he just needed to stop. So I put my foot down one day when we were grocery shopping and told him that I was NOT going to buy diapers for him any more. He can wear pull-ups at night if he has accidents, but he's not going to wear them during the day. It took two days of me reminding him every half an hour to go potty. I didn't give him a choice the first day and it was something of a fight. I just announced it to be potty time, put him on the toilet, and stood there with him (sometimes running water in the sink) for at least a couple of minutes. He was rewarded with stickers to put on a chart when he actually went, extra stickers for remembering to wash his hands and flush... By the second day he was going without having to be put there. By the third day he was remembering to go without having to be asked. Now two months later he hasn't had a single accident! My older two were naked trained and I really do prefer the method. Either loose boxers or just a teeshirt for a day or three and they're potty trained! I didn't do that with Michael because I have state workers coming to the house unexpectedly all the time (to visit foster children staying here, to drop off kids or pick them up, etc...) and they frown on that sort of thing with foster children in the house. *shrugs*
Charmin has a GREAT potty training resource for free! I've used this with my middle two successfully - the stickers were great fun and the book was endlessly interesting. It also made great material to keep them sitting on the toilet long enough to go - they'd read the book while going. It even comes with a measuring thing you hang on your TP wrack that shows them how much toilet paper to use:
http://www.samples.aohosting.net/campaign/Charmin_PTK