londrum - 8:12 am on Jul 7, 2010 (gmt 0)
i still think that a lot of the ups and downs can be attributed to them creating the index from scratch. which means they had to run through the iterations a few times to weigh all the backlinks in. remember that at the same time all this happened, GMT started showing old data in it's speed tests, old data in its page errors (mine included pages which hadn't existed for months) - and now its showing vastly inflated numbers of backlinks, whatever that means. those errors show that it wasn't simply an algo change. it was something to do with the age of pages it was indexing.
that can maybe explain why so many spam sites got a boost, and quality sites started tanking. because i would imagine that the first few iterations would largely be based on the numbers of links, before subsequent ones discounted them.