Google Florida Update
Here is a very nice article on some changes to the Google index, which seem to apply mostly to commercial terms that are full of search-engine-optimized sites. In short, it seems like Google has a list of keywords that are over optimized and in that case add an algorithm over the standard ones that throw out sites that seem (!seem, not are) to be search engine optimized.

Want a real movie theater chair in your home theater? http://www.SeatsAndChairs.com
I was in the top 5 listings under the search term…
“home theater chairs”, now I am completely gone!
Home theater chairs is EXACTLY what we do.
I was listed #3 on Nov. 21st. # 54 on Nov. 22nd, and completely gone from the listing on Nov. 24th.
My business has dropped 80%!!!
Gone from Google, gone from Yahoo. Thanks for nothing Florida Google update!
I emailed Yahoo 3 times, guess what they recommended? Pay for an AdWords account.
Yes I am mad at Google and Yahoo.
I am a small business with 2 working owners and 1 employee.
So much for a great end of year jump in sales.
HoHoHo, the jokes on us web site/ e-commerce owners for believing in the new technology.
Looks like the light at the end of the tunnel was a gorilla with a flashlight, wearing a Google.com t-shirt.
SEO after the Google Florida Update
In mid-November Google deployed the first major update in months, now known as the ‘Florida’ update. Previous updates have introduced changes to Google’s scoring algorithm and adjusted spam filters - filters designed to catch sites using hidden-text, l…
I think initially they created on overoptimization filter which dropped out those results which were artificially there.
Then after that they went and reranked the results looking for inter connectivity of the results and began applying the ontology algorithm.
Those results which were not well interconnected fell out and through each respidering the relevant results lifted again to the top of search results.
i agree with aaron, as usual.