its so fast because internet is very dynamic and thousands of new sites are born every day....And google s strictly concerned about the contents in a website.if a website is not up to the level they expect from the previous page rank ,they will surely reduce the rank

Google updates public PR every 3 months. However real PR updates on regular basis and hidden from public view. Anyway, why does this problem disturb you?

that why Google is number one

I've kinda been researching this for a bit. I noticed that over the past few months there have been several page rank changes to many different sites. Specifically social bookmarking sites. I have several hundred of them cataloged and noticed a difference of sometimes 2 levels of page ranking in a short time, perhaps 2 months.

I haven't arrived at any conclusions yet, but now I'm intrigued about private vs. public page rank. I hadn't heard of that before. Very interesting!

Vance

Google updates pr but not frequently. Before it takes 3-4 months but lately you can't predict on the exact month because sometimes they update pr in every 2 months.

If you are talking about Page Rank (PR) then Google update it once in three month and other changes in rankings and result pages are continuous process.

No one knows what's the reason behind it but it's google algorithm. All of us didn't know why they keep of updating backlinks and pr.

Google update PR frequently because there are many thousands of pages added every day on internet and new sites pages links to many pages and so it won't be a good idea to update the less frequently.

completely agree with bob and cscgal, PR are meaningless, but they have much value for advertisers. Basically, bob is right, PR are done to find out the sites selling links. I have noticed after every update that many sites gets impact due to selling links. Selling links can hurt your site page rank on google.

if google put a green bar then it have meaning in search engine and also for people who use it ...because it present site relevancy .