I just wanted to point you folks over to two threads that Alan Webb (a colleague and respected SEO based in Germany) started on the topic of major search results changes in terms of rankings. I'll quote the post and then link to them below.
Many webmasters in the thread above are reporting significant drops in traffic, up to 80% in some cases within the last 24 hours. In contrast others are reporting significant rises in the SERPs which indicates a big change (which imo is not sandbox related).
Rather than having a "I've dropped/risen too" thread, perhaps it is a good idea to attempt to work out what has been happening. I personally have seen big changes on numerous travel booking related sites. One of the theories appears to be too high keyword density. This may have some merit, as on some sites ranking drops are not across the board on all themes/phrases. So it could be that templates focusing on one term have a much higher density than others. I'll certainly be looking into this. I'm also wondering if this is somehow theme related as as I've mentioned it defintely has affected the travel theme. or perhaps it is based on just highly competitive terms as a whole.
It would also be interesting to see if there is a concensus from those sites that have lost traffic on..
1. Are they affiliate sites with many links to the affilate host. 2. Do they have satelite domains which they cross link/one way link with sites particularly on the same ip c-block. 3. Are the drop in serps keyword specific or site wide. 4. Are some inbound links on mass from single domains. For example, a great number links from a footer link on a major site. 5. Have changes been made to keyword density recently. 6. Is there a distinction in ranking between major and minor terms. 7. Has there been any PR changes or backward link changes.
Google isnt likely to give us the direct answer, but maybe they wont need to if we work together in cracking this change.
If your site has been affected from wednesdays update, it would be helpful for all, if you could perhaps answer the 7 points above relating to your own site.