I think inless you're selling the exact same item as someone else, and there are a million of them (say, a search on "socks") it doesn't matter much. If I have an item listed and there are only two, three, or five on the entire eBay system (and many times that's the case), would it really matter where my item appeared? It's still going to be visible on the first page. BM is really only going to cause grief to the drop shippers who all sell the same item. In this case, their rating will determine how they are advantaged. This is why I could care less about BM. It doesn't affect me, and never will.
BM is there to disadvantage the shitty sellers with poor customer ratings. I think hoping to either 1) drive them away, or 2) make them clean up their act.