Is blog spam any different than email spam? As a phenomenon it's basically the same. Maybe not as intense, since spam email is 80+% of email volume while blog spam has yet to reach 50%. Any channel that can be corrupted will be corrupted. And then the corruption is beaten back and it's impact is minimized.
So Doc Searls' post on blog spam is fine and good. We do need to fight it. But it all feels like a repeat of the email spam problem, or the junk mail problem or the phone solicitation problem.
If anything, the impact of email spam was easily 100 times more harmful than blog spam because email is 10 times more important to productivity and is used by probably 100 times more people than blogs. Yet we muddled through, didn't we? So I'm not that worried about blog spam in the end.
Online marketing goes in cycles. Any given technique "works" - ie. reaches people and generates interest - for a short period of time - perhaps under 2 years. I.e. banner ads, email, newsletters, text ads, blog marketing, podcasts, tagging, etc. etc. They all open with a bang and go out with a whimper. Marketers jump in, and the return on the medium regresses. Spammers jump in and increase the noise for every medium. Technologists then fight the spammers.
The effectiveness of any marketing technique rarely lasts more than 30 months. And then people go back to what worked four or five years ago... direct mail, sending executives FedEX boxes, etc...
The inherent value of the blog medium will survive while the marketing corruption cycle spins around it.