Seems like the spammers have found the web equivalent of an smtp open relay.
For example:
[
http://wiki.cs.uiuc.edu/VisualWorks/DOWNLOAD/sb/index.htm sitz bath]
[
http://www.buddy4u.com/view/?u=monophonic+ringtone monophonic ringtone]
[
http://www.buddyprofile.com/viewprofile.php?username=nextelringtone
nextel ringtone]
These are links to legitimate sites that perform poor input
validation... The spammers have managed to convert the pages into http
redirects.
Because of how the various search engines work a link to a redirect
page is just as good as a link to the redirect target.
Since the spammers can make an infinite number of unique URLs at these
sites, blocking the exact URL is pointless. So right now our only
choices are to block legitimate sites because their poor hygiene
allows them to be used as a spam-bouncer, or allow ourselves to be
spammed with these sites and contribute to the declining usefulness of
the internet.
Things like this make nofollow more attractive all the time. Has
there ever been any discussion on perhaps allowing a white-list for
non-spam sites that we won't no-follow? This would be useful for
wikis who don't want to kill all their externals with no-follow.