I've got fed up having to delete spam comment posts from China in the comments section on a daily basis, so I've just turned on comment moderation: no more instant posting.
I don't want to have to do this: to me, it kind of defeats the purpose of the comments area - if you don't know when your comment is going to appear, and there seems to be a conversation going on in the comments section, moderation feels like it's disconnecting you from the discussion. You don't know when your post is going to appear, and you don't know who else has also commented, and if they've already made the point you were going to...when your comment if finally approved, it can look as though you're disregarding the points made before you, by others. It can make you look accidentally rude.
But, allowing free commenting means regular spam postings (usually in the middle of the night for me), and the longer they sit on a post, the more it feels like the blog is unmanaged and uncared for.
What do you think? Better to have unmoderated posting, and a few spam comments, or better to have moderated, and no spam? Do you notice spam comments on a blog? Does it make you feel that blog is slightly abandoned if you do see them? How long would a spam comment have to be viewable/not deleted, before you would start to think the blog owner doesn't care?