If ever I wanted proof that advertising/spamming is an evil twisting of communication's intent (true, real interaction between people), spam blog comments would convince me of it.
Case in point:
Hi ________. Can I find any information on http://www.__________.com here? My friend said to check out [insert recent post title here]... for information on _________ but this does not seem like the most relevant of blogs. I like cruzing through your site but maybe search engines might have more information. Need to come back later though...great blogs!
Nice. A touch of personalized info and reference, informal style, some misspelling and grammar errors, and bingo: some poor blogger is deluded into believing someone reads and likes their blog. If the ad perpetrator is really lucky, the blogger will now post something about topic X in hopes of luring the reader back.
If I choose not to put ads on my blog (not saying they'll never be there, just that I don't want to put any on right now), I definitely don't want someone else putting ads on my site. Grrr.