You'd be surprised - last night, spammers posted up to 15 posts within 2 minutes of registration. I don't know how they do that, but they did ... in fact, about 30 different ones did. It was awful and time-consuming to deal with, but at least it was all stuck in the newbie forum. 5 to 10 posts would definitely NOT be enough. In fact, while I was deleting one bunch of spammer messages, another spammer was able to get up to 35 in less than 5 minutes!