At what point do I blacklist all email from hotmail.com?

I've gotten 5 spams verified (by SPF) from hotmail in the last 6 days. I reported the first 4. Since November 1 I've only gotten legit email from one hotmail account. Email I would not have minded missing. Hotmail is now a significant source of spam my filters don't catch. At what point to I blacklist all email from hotmail?

Do any legitimate users still use hotmail?

I made up a new way of blocking spam: MTX records

http://www.chaosreigns.com/mtx/

MTX records are just DNS A records on your DNS server stating that an IP is a legitimate mail transmitter.

There is a SpamAssassin plugin for it on that page.