Deep linking to a post where Ollie was answering some questions about balance changes. I think this was the last really major change to how it works overall but it was still tunable.
There is more technical info on the system and changes, there in the thread. Luca and James both comment on aspects of the system.
Discussion about the tuning/balancing:
If you look at threads that have linked into these threads (now this one too) you can probably find too many hours of reading.