I've not had much of a problem with this, primarily because of the low traffic here, but today I had to delete a comment from my most recent posting because it was simply and only spam.
My content policy is clearly placed on the left hand side of this screen. It specifically notes that commercial announcements and spam are going to be deleted. If you are trying to generate hits for a website via spam links, it won't do any good to post them here. I'll just take them down.
I have a free speech policy on topical debate. If you disagree with me, swear, throw around racial or religious epithets, or attack my positions or character great. Just make sure it's topical. Anything someone says in a comment, in my view, reflects on them. I denounce objectionable statements rather than simply deleting them.
But I'm not going to leave spam links on my blog. Sorry.