I have several friends in the preprof program. According to one of them, who's a junior this year, it's sometimes a crapshoot - i.e. in his words, some of the people that get in he didn't think would make good doctors and eventually did drop the program, and some other friends he has now he thought totally should have been in the program.
Either way, this year has been different as far as taking the MCATs and applying out goes. Traditionally a lot of the preprofs would apply out anyway, because they could hold their scores at AMCAS and only apply out if they did well. You need a 32 to stay in the program. If you don't get a 32 on the MCAT you lose your guaranteed spot and have to apply the regular way. However, with the score hold option, people could choose to release their scores only if they did better than a 32.
This year AMCAS has done away with the hold option and so many people decided not to take the MCAT for fear of not getting a 32. From the junior preprof class, I believe there are only maybe 2 applying out (as opposed to more in earlier years). The way it works I think is that you fill out the AMCAS as normal and have an "interview" and "tour" at the Case med school, but you're already accepted. Now there's no hiding your score, Case med will see your score if you take the MCAT.
The great thing about the program is that without having to take the MCAT, you really don't have that stress. You also have the freedom to take it a little easier, go abroad without worrying about the application process, etc.
I'm sure you already know, but in case you don't, you have two interviews, one with an undergrad person and one with an interviewer from the medical school. Because it's basically interviewing for undergrad and med school both, just treat the interview day as you would if you actually were interviewing for med school, and make sure you can explain why you want to go into medicine.
Good luck!