Google Dance is a rapid change sites do in the google search engine positions that can vary from one to other google data centers.
It is not a perfect method to know wich will be the future search engine position but it is very useful to show a trend in it.
Using the right tool: www.seochat.com/googledance/ and comparing the serp (Search engine result pages) for 3 main Google datacenter around the world (www.google.com , www2.google.com , www3.google.com) and a 4th datacenter (i.e.: google france if your site is in French Language) we can have interesting indications about the goodness of our seo work.
In this exact moment a site on which I'm working after a lot of months in 4th position for the main keyword and after a lot of changes to html code in order to avoid errors and duplicate urls,keywords,title and wathever seems going back to the first position. I can say that because in the French serp it is 2nd but on the other data centers it's just first! And the trend is going better week after week. Now I expect that it will be first on all data centers and so also on the one of my interest.

Here it is another interesting tool: www.google-dance-tool.com , it allows to make comparison between more Google data centers.

A very detailed technical article about google dance and The Index Update of the Google Search Engine.

Another interesting article about the so called "Google Dance": http://www.webworkshop.net/google-dance.html

Check out the tool suggested in the Google Dance Tools of our Seo Directory