In the Google Groups, Adam Lasnik posted a comment that included a statement that Google is working on something to allow crawling of pages that require a login. Here is the portion of Adam's post in which he makes the statement:
On a happier note, my colleagues and I are working on an arrangement which I think you'll be pleased with... balancing many Webmasters' interest in requiring community membership or signin to content-rich pages while still showing content in Google's search results. Stay tuned :) (we'll make an announcement in the Webmaster Central blog)
Now this is big news in my view. This will expose a lot of additional content to the world if they do take this step. You would have to imagine that they would include some method of tagging this content, so when it shows up in the search results it will be identified as subscription based content.
This type of step is consistent with Google's drive to index all the world's information. So the next question is: When? We will just have to wait and see.