It is best not to tell people how to do this or give them ideas about it.  The auto-increment settings solve nothing.  They just make it possible for you to fail to notice how badly messed up your data is getting.  In addition, there is absolutely nothing to gain from writing to more than one of the servers at a time.  And there are many edge cases when things can go horribly wrong.

I advise readers to get a copy of High Performance MySQL, Second Edition and read the replication chapter twice.