Yes, +Matt Cutts
, of course you and the rest of the Google team reserve the right to adapt your criteria when new types of 'spam' (because the definition is ambiguous and subjective) come up, but webmasters can do as much in regard to Google. Not everyone agrees with Google's views of the Web world.
However, the recent insistence on a heavy use of nofollow links on pretty much any kind of links worries me not just as a web marketer and a freelance professional, but even as a computer scientist -- I'm sure you know, Matt, that every webpage is a node in the Web graph; nofollow links disrupt connections between nodes and some nodes may become isolated.
The recent action against MyBlogGuest lead many website owners to nofollow ALL (or nearly all) outbound links as a reaction to the fear your Webspam team might deem their guest posts and editorial links spammy. You can imagine what would happen if everybody starts to nofollow every link, right?
And for a change of topic, I really don't like the "rel=nofollow" attribute on paid links. Something like "rel=advertising" would make much more sense, semantically speaking. ;)
Have a nice weekend, Matt. I just hope I provided a little bit of food for thought.