My daughter is 20 months old and has had similar problems since she was about 5 months old though. She'd go to sleep okay, just not stay asleep. Right now she is like Tara's son and sleeps on the floor, but I dont' care either cause she sleeps all night. We went to the toddler bed at 14 months and she stayed in it just fine till she was about 17 or 18 months. But the problem was that she'd wake up during the night and I've have to go pat her back to sleep too. I wouldn't care if she came into my bed, but she cannot sleep with anyone else-she kicks, punches, etc. and while I could live with that, she can't and she cries, screams, and pushes anything in her way. We took her to a sleep clinic at 16 months and they said just keep walking her back to her bed, don't say anything, and she'll stop. Well after almost 2 months of that I gave up and she basically came in my bed and my husband moved to the couch (he cant' deal with the kicking and she can't deal with how much he moves). Then she started preschool in September and so I didn't want to make any changes so I waited about a month. Then I decided that she could sleep where she wanted to, but not in my bed. So she took her blankie and stuffed alligator and slept on the floor next to my bed. Everynight since then I'll read her a story in her bed, laying down with her, then when I'm down she climbs out of her bed with her items (which are now the blankie, stuffed alligator and a stuffed Buzz), makes her way over to the floor next to my bed and goes to sleep. She can climb in my bed and she knows that, but she chooses to stay on the floor. When the alarm goes off at 6am she climbs into my bed and we watch the Wiggles together before we get up to get ready for school. Right now she seems happy with this arrangement, though I'm hoping that she'll realize her bed is more comfortable than the floor and she'll start sleeping in there. We just set up a blanket on the floor for her though since she hasn't come to that conclusion yet and we felt bad watching her sleep on the rough carpet.
Oh, incidentally, the preschool she goes to is a Montessori school and I was talking with her teacher about her sleep habits and how she sleeps on the floor, not her bed and her teacher said that one of the Montessori theories is putting kids in a bed on the floor basically from birth. She said they use a regular mattress on the floor instead of a crib and once the kids become mobile they're often found sleeping next to the toy box, by the door, in the closet, etc. Granted, she doesn't have any kids yet, so I don't really know anyone who has practiced this from birth to know how it goes, but I thought it was interesting that people actually advocate what my daughter does, when I thought it was sorta a bad thing.