I just spotted that Google Webmaster Central announced they are supporting a new tag, rel=canonical, that allows sites to specify which URLs on your site are the canonical versions. They explain it in all of the gory detail on their blog, but in short when you have multiple versions of a single page, this tag will allow you to say that all of these urls should now be considered the single, canonical version with all the pagerank and SEOness passing to that one URL.
If this system really works, then this is a huge gift to both SEO consultants and their clients. Now when you tell the engineers who didn’t hire you and who are pissed that they have to spend time doing that stupid SEO crap when they could be building the next Twitter that they have to 301 redirect 10 million urls and noindex 50 million, you can say “or just add a tag in the <head> section”. Should make for a friendlier conversation.
Of course there is no guarantee this tag will work well. Google says it will “take your preference in conjunction with other signals”. In other words, maybe it will work but if that dupe URL has a ton of inbound links to it, maybe it won’t.
And of course Joost De Valk already has a Canonical URL Links WordPress Plugin. I love that guy.