The most heavy solution would be to force edits by logged in users and have a user only creatable by an administrator.
There have also been some nice hacks floating about to allow anonymous edits only to talk pages. I rather like the combination of these ideas for the beginnings of spam prevention.
Then denying the wholesale dump of links into talk pages via some other spam prevention mechanism.
Also, it would be nice to rewrite talk pages into a folder and tell google via robots.txt not to rank anything in that folder.
But all of this just adds layers upon layers of complexity.. =/