Google sort of encourages this kind of cloaking. It's called First Click Free.
http://www.google.com/support/webmasters/bin/answer.py?hl=en...
http://www.google.com/support/webmasters/bin/answer.py?hl=en...
I can't count the number of times I've seen an interesting article on Reddit or HN, clicked through, found myself butting up against a paywall, and then just Googled the title and been able to read the whole thing for free. You think that these companies would suddenly put their whole archives online for free if they didn't get a bunch of search traffic for it?