I'm still looking to do this. Been a very busy summer so still haven't pulled the trigger yet.
My car came from the PO with BC Racing coilovers. My mechanic says that I can do a lot better. I think I need to do some more homework on them before spending money and ditching them. I know a few people using BC Racing setups that are pretty happy for back road carving.
And over the summer, very few used setups for the M have popped up for sale on the forums.