As with ad blockers, the proportion of "savvy" web users is so small as to effectively not exist.
It would be trivial for someone to write a Firefox plugin so that every page request on a "protected" domain is given a Google referrer (e.g. https://addons.mozilla.org/en-US/firefox/addon/953). But unless someone builds this functionality by default into a browser with significant market share, it won't be worth it for the content provider to try to stop.
Experts Exchange actually include the "member-only information" at the bottom of the page. The top says: "Sorry, you need to be registered to view this!" but it's a lie.
Are you sure? I've read in the Google policies that you're supposed to serve the same content to Googlebot as your users or you're penalized in PageRank.
Correct. Technically in this case they are in the clear because what people see on Google is what they will get when they click on the link.
What is currently penalized is when you do this without checking the referrer and show everyone a sign-up screen. That'll get you penalized in a serious hurry.
If so, this might not be so great for publishers, as savvy users will just ALWAYS access their content via Google searches.