Google is mainly helping the society so you should understand this thing, if you are building any website then it should be helpful to the society mainly.
No one really knows what happens during the Google algorithm updates, so chances are you'll just get a bunch of educated guesses. Also, it doesn't matter what's happened in the past, only what's recently happened and most recently Google changed their algo so that useless content sites have less weight in their search engine.
Do you have google earth, google desktop, google sketchup or any other google software installed on your computer? It sounds like this is the software that keeps those programs up to date by downloading new versions for you.
Give this presentation a try from SEOmoz, it may help: http://www.slideshare.net/randfish/the-evolution-of-googles-rankings
The new update Google has published has refined the old SERP ranking algorithms and makes search results more accurate to the search query by eliminating duplicate content and several other important things.
I diont think anybody from here can detailed the updates for you but more or less from 1990 to the present Google has been striving so hard to bring good search experience for their users.
Google updates it's algorithm every 3 to 4 months in a year, that is what is called google update However its like the Big Brother in the novel "1984", where the Big Brother is watching you, always and you never know what his next move will be. So google has never disclosed its secret of algorithm, however many experts have guessed lot of opinions by the number of count of the backlinks you have to one particular site. And yes those opinions have come true, as well