I have been putting my 24 month old on the potty since April, and getting mixed results. Sometimes she just won't sit. I brought a stool in as a table and put different toys on it (things that were too big to drop in the potty - she loves to do that ugh). Since we are on a super tight budget, my goal is just to avoid throwing out diapers that still are barely wet but have been pooped in. I have her eat meals in her high chair, buckled in, and she will make a fuss to get down even if she's not done eating if she has to go, so then I put her straight on the potty, and sometimes feed her some yummy fruit or snack so she will relax and stay on the potty. That's been working fairly well. She still seems to prefer pooping in diapers because it's easier to push standing up, but her bottom gets red every time.
Yesterday at her ped's office, she was reluctant to get in the car, so we went back in to use the toddler sized porcelain potty, and it took a good 20 mins but she finally went!
I usually read a story and/or sing a little made up song about how we go poo poo in the potty but don't really focus on what she's doing, and when she goes pee or poo, she turns and looks at me, and I look at her with wide eyes, and ask, "Did you just go peepee in the potty!! YAY!! YOU DID IT!!" Sometimes I whisper it in excitement, sometimes I shout it and do a little dance. I change it up so she gets excited trying to anticipate what reaction she'll get. At home she gets one tiny candy for pee and two for poo, and the same number of smiley stickers go up on her sticker chart, plus she always wants one on her knee. She reminds me if I forget.
At home she'll still rarely ask to go on the potty, but sometimes she does. She almost never willingly walks to the potty when she has to poop. She'd rather go play until she's done, and even then still doesn't ask to be changed. Occasionally she'll sit on the potty and not poop even though I KNOW she needs to, but someone mentioned the relaxation factor in another thread, and that is probably what I need to work on. I hate it after we spend 30 mins in the bathroom only to have her poop the instant I put her diaper on.