I'll buy that the engines have a way to differentiate between "unnatural" and "natural" recip linking. You've won me over on that. But that doesn't mean they aren't devaluing even what they deem to be natural recips. They may be accepting them as valid, but weighting them less vs. the other variables that go into ranking sites. Fair enough? I read a decent article about this very thing the other day in an SEO newsletter (can't remember the author's name). They ran months-long tests on a large number of sites to reach the conclusion. But hey, who knows?