Thought I'd make a quick note here about spam again, as one just managed to get past the normally quite good filters here.
Spam, as far as this blog is concerned, is not just sales pitches or link farm posts. It's basically any comment that tries to hijack the subject to spout whatever the commenter wants to talk about. One and the same comment could conceivably be spam when posted on one post, and perfectly fine when posted on another.
Those kinds of comments is just like that guy at every conference; the one that wants to ask the speaker a question only to spend five minutes droning on about some subject that has nothing whatsoever to do with the presentation. Meanwhile the entire room silently sits there, hoping he'll have heart attack, stroke or an inopportune bowel movement — anything to make him shut up already.