Jane_Doe - 10:37 pm on Feb 27, 2011 (gmt 0)
Nobody even knows what happened exactly with the algo change at this point. If you do, please let us know and you will get a gold star.
Here is my try for the star -
They discounted some types of lower quality back links. In some cases these back links had counteracted spam penalties. But with the back link pluses now gone, the negatives outweighed the positives for some sites and the spam penalties kicked in. Sites that had a mix of high quality and low quality backlinks for the most part survived, but may have dropped some positions. Sites with only the types of low quality back links, compared to their competitors, dropped a lot.
Individual pages with discounted back links dropped some positions, and the pages with discounted back links, no high quality back links and spam penalties dropped like rocks.
I think there is more to it, but most of it has already been reported here by other posters.