Blog spam

I've noticed a scary trend in the spam I've been receiving in the comments and trackbacks of this blog: they've started using plausible non-spam domains (businesses, organizations -- I'm not going to do their work for them by mentioning the names here) for obvious spam content (poker, drugs). This makes it hard to tell if I should blacklist the domains. Have they illegally taken over some machines? Cybersquatting? What if the organization ever gets the name back -- they'll be blacklisted everywhere. I guess I can't afford to be charitable -- into the reject pile they go.