>>>
Is it more user-friendly to provide
an explicit "Sign In" link and hide the links to the registration-only
content, or to display links to that content and then provoke login once
the user clicks such a link?


In my experience designing quite a few complex sites, and backed by a number of usability tests, I would say your instincts are correct. Users will not register for something until they see the benefit of it. The only way they can see the benefit is if you let them see samples of the content they will receive before registering. This is a win-win situation for the company as well, because using this technique typically results in much higher rates of registration than if you require registration first.

As further evidence, you might note that nearly every shopping based site allows users to place items in their shopping cart without registering or logging in. Once they are ready to purchase, then login or registration is required.

With regard to content based sites, both the NY Times and the Boston Globe (among many others) have moved to this kind of model.
-matt

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