Google updates PR constantly because it wants to determine which sites are valuable or not. And I'm not a big fan of PR. The display PR is simply a rounded off value determined from a logarithmic scale that can be easily manipulated.
Google might be tracking the sites which are involved in buying and selling links, Google can penalize or drop their page rank anytime. This could be the reason Google might be updating the Page rank so frequently.
Yes, they do ... but, as mokmok pointed out, new pages are being created and deleted every single day, new links are being added and removed every day, so there's ALWAYS going to be flucation as pagerank is continuously created and deleted.
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
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!
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.
There are thousands of websites on the internet growing up each day, google keeps on changing Algorithm from time to time to make sure that the people get the most relevant information whenever they Search for it.