I think this thread has reached a size where it's just not practical for people to read the whole thing, it really ought to be broken down into a number of different threads. I know that working a busy job I would never have had time to read this whole thing whilst doing the prep for the assessment days at the same time and I don't feel that it would be necessary either. The useful info on this thread is probably the links to sites where you can practice stage 1 tests so it would be really handy if that could be put into another thread. For stage 2 you cannot do any prep so there's nothing you need to know and stage 3 is an interview so just prepare for an interview as you would any other interview. I would say that HR give all the info you need.
Don't get me wrong I do think it's a decent forum thread, it's nice to read about people who are going through the same process as you are but I just don't think it's practical or necessary for people to read the whole thing. Unfortunately a downfall of the thread is that it's easy for people to give out of date information, HR can easily change the application process, pretty much everything I had read on this forum about stage 2 was completely inaccurate by the time I got there so I would be nervous about offering advice to applicants and advising on what happens on the day, it's best to ask HR and not to rely too much on info from past applicants.