Talking about the point about 'O's being good preparation for 'A's, i'd just like to share my personal experience. In terms of exam environment and the fear of screwing up, yes i'd say it is probably the best prep. However, the 'O's has absolutely nothing on the 'A's in terms of academic material. The 'A's is much deeper, broader and yes, harder than the 'O's. I remember not studying much and hitting an 8 for 'O's, maybe with more mugging and some luck i could've easily gotten a 6. Its a different world in JC though. I see fellow 8 pointers struggling to promote and cope with the workload and sheer amount of knowledge and skill sets required. Even now, some of these people are still hoping to just pass their prelims (which just ended for me), which isn't the way to go.
Do not ever make the mistake of thinking you can do shittily for prelims in 'A's and suddenly get all As for the actual thing. No, doesn't happen that way. In short, the academic prep for 'O's is nothing compared to the 'A's. It'll be a whole new world, especially with THE most hated subject in JC, the infamous project work, where you work like a dog to get an A for just a H1 subject, yet the world seems to fall apart when you get a 'mediocre' B. I know, i've been there. It happened to me. You can't do well in JC without consistent work. Absolutely not. You'd have to be damn smart to be able to get 3As for 'A's after struggling to promote and then starting to work hard only in march of your JC2 year.
Some of you all might feel this is out of point, that i'm trying to scare all the 'O' levellers just because i'm being a bastard. Let me clarify that my intentions were not to do that, yes it was meant to scare them, but only to prepare them for the life that will come should they want to and are able to qualify to enter JC. I don't want these guys to take the same path of destruction that many of my friends took after finishing the 'O's. Cheers all!