AFAIK The only major change has been the core book. If you're really curious, look at the errata for Sunward et all to see what mistakes they've made.
The core book is what I meant! Sorry, I should've been more clear about that.
I know there were significant changes (initiative and the d100 system among others) just from listening to the APs so my concern is getting 4 copies of the core book to pass around to my group and then getting another big mechanics change errata'd in.
After thinking about it some more this afternoon, I'm gonna do it anyways because the best way to convince my group to play a game is to put a book in their hands and let them absorb the material through osmosis.