Many people wonder why their home page (or other pages') PR drop's when Google does it's PR updates. In a lot of cases it is due to the "Google Cascade". The page PR is derived frow a calculation based on the number on links to the page and the PR of the pages containing those links (plus other factors). So if you get links to your home page from high PR pages, the PR of your home page will also increase. Yehhaa! but.. just suppose that the reason that the high PR page linking to your home page has achived it's high PR through paid links... and the owner of that page decides he doesn't want to pay for those links anymore, now that his site has a high PR of it's own and cancels his payment for the paid links site. Well.. when the next PR update comes around.. his pages drop in PR because he is no longer linked to the site that was giving him the (juice) to maintain his high PR. This low PR is then cascaded down to your site home page links and so on right down the chain of links, so many sites can end up dropping in PR because one site lost it's high PR ranking. Booo! I call this the "Google Cascade". Of course there are many other factors, not just paid links that can cause the same effect, domains not being renewed, links being broken or removed. Just something to think about, if you are actively trying to increase your PR through link building. J
yes, you have a point, but also, google changes it's algo to devaluate some types of links, in return, those links count less for your site and other sites in the chain.
Yes, buying or selling links is the main factor when it comes to a sudden drop in PR. Google penalizes PR of sites that sell or buy links.
This post is indexed in Google ALREADY... Check it out: The Google Cascade Just over 3 hours... How cool is that J
This is why it is important to keep building links even after you achieve the search engine results you are after. This distances you from your competition and also protects you against changes in rank of the websites that link to you. If you have a strong enough link profile, changes in other websites will affect you very little. A lot of times a website keeps its rankings even after they lose rankings. It takes a while for the search engines to even realize that the links were even removed. The search engine spiders are more concerned with finding new links.