From what I remember of their "signing up" process it should be an easy add-on to the program to have new members first "blog" wait in moderation for approval. Then they need to check email/IP addresses and block them from signing up, because I'm willing to bet that most of the spam is coming from one or two people.
blocking IPs isn't really that effective. There are ways to change your IP and with the use of proxies, you can get an IP address from anywhere in the world. I think a probationary period for new accounts is the best solution.