Thoughts on the certification thing:
Mailing everyone would probably be bad. :) But I suspect you could do pretty well by taking a statistical sample--and at that level, it's sort of interesting.
But, in general, I'm not sure it's a great idea at all. As dria said, you don't need the machine to tell you who you know about.
A thought, though. It's in some ways interesting to think less in terms of the people who everybody recognizes, and more in terms of the people who you don't recognize. Brin's book EARTH had a system in which people had a reliability rating which appeared next to their posts--and that's important when everybody can say things.
I think there's little value to a system in which people are rated based on how well known they are, but much more when you can find out how respected their opinions on a certain subject are. I mean--you don't know me from Adam, but if you shopped around a bit, you might find out I've got some good knowledge of Emacs, Perl, Java, and good specific (non-normal) knowledge of scary XSL tricks, scary SQL tricks, and functional programming languages. And, more importantly, that I started but didn't finish writing nnimap for Gnus. (Which cuts me both ways. :)
Knowing these things makes it much more easier to figure out what things I say are reasonable, and what's bunk.
I think the main thing is that none of this stuff should be in any way mandatory--and it's only necessary for those faces you haven't seen before, when there are a *lot* of faces.
Now that I understand the diaries are the main important advogato feature, I see why it's even a question. And I'd say that what you really want is a way to rate somebody's "reliability" or whatnot any time you read something from them--assuming that you only do so when you know it's good stuff or bunk.
And once you have that, the averages ought to work out reasonably. Which only leaves the problems of "how do you convince people to do this, and do it right?" and "how do you do it without getting in the way?"
Which turns out to be really hard, of course. :)