How often does Google change ranking strategy ?

i think it is a constant process, I suppose that it will vary regularly in order to prevent spammers

 

I think no one can give a accurate answer as only google knows about it. When and what google changes in search results strategy, only google can tell.

 

Well, there are minor tweaks done almost constantly

 

they indexed post in less than 60 seconds in famous blogs so there. Constant per second changes. My previous experiment was to get my PR5 blog indexed a post in 5 minutes, but I was shocked to see it in the SERP's with a tag "less than a minute ago" next to it. indicating it got indexed in less than 60 seconds

 

I think google indexes alot of junk pages (dupe content) then it should. It must be all this "web 2.0" stuff recently where you have a pages on a site with duplicates templates and maby the difference from one page to another might be short line of text and page title. For example a youtube video, the video is the content, but from 1 video page to another its all Dupe.most users don't put much text in the descriptions other then "Lol this is funny please watch"