I'm probably a bit late here, but here's my 2 cents worth. I'm currently going through the caseload program at Casey, although I have opted for a hospital birth. I did the same thing with DD 2 years ago and had no problems. Although I have opted for a hospital birth, my midwife has said that I can still change my mind if I want to (DH is not interested though!). So, once you're in the caseload program, you don't need to decide straight away. I guess if you decided that the rules were too much, or you didn't click with the midwife you were allocated, you could always change your mind and go with the IM.

I have heard that caseload is not offered unless you ask for it though, and it does fill up quickly.