The attribute rel="nofollow" was
designed to let bloggers, discussion forum maintainers etc. turn URLs
to links in posted texts without thereby giving search engine boosting
to the URLs.[...]
I thought it was more for where third parties were allowed to post to
your website - such as when commenting on a blog.
I think that's what I wrote about. I have trimmed your quotation of my
words to indicate this. "Posted texts" covers all postings but of course
most importantly those by outsiders - you don't expect yourself or your
coworkers to post crap.
So its intended as an
anti-spam measure as some blogs get spammed a lot
More or less, though it works rather indirectly if at all: it does not
prevent anyone from spamming, just tries to decrease the benefits of
spamming and thereby motivation to spam.
Its also a way of indicating that a link might be a paid link -
something which google is against, but will tolerate if its flagged as
nofollow.
Google cannot really know whether a link is paid or not. It can only
make guesses, based on heuristics. And the idea of using rel="nofollow"
for paid links will probably lose two ways. First, who would pay you for
putting up links if you deliberately tried to prevent the links from
working well (from the payer's perspective)?
Second, do you trust Google? The idea of flagging paid links as paid is
comparable to the idea (suggested as early as 2004-04-01 by a reputable
net personality) of setting up a top-level domain .crime where only
criminal content is allowed, with the promise that crimes made there
will not be investigated and punished.