Links from one site to another not only help Google find a target site when it is new but also contribute to the target site’s PageRank. Among other considerations, Google’s ranking algorithm measures each page’s popularity based on the number of other pages that link to it. The theory is that if Page A puts up a link to Page B, there must be something worthwhile on Page B. If 100 sites link to Page B, the target page becomes more worthy in Google’s eyes. If 100,000 links to Page B are scattered around the Web, Page B must really have something going for it. From Google’s viewpoint, Page B must have special value to Google’s users, and therefore deserves higher positioning on the search results page when it matches the search keywords.

Google doesn’t rely totally on counting backlinks, by any means. Many other page-analysis calculations take place when determining PageRank. Even the counting of backlinks is more complex than it seems at first, because Google also evaluates the worthiness of the referring pages (the pages linking to Page B) to determine how important those backlinks are.

The outcome of all this evaluation, from the user’s viewpoint, is a sense of the living network underlying all Web pages and sites. No single page in the Google index exists in isolation — they’re all embedded in a deeply complex matrix of connectivity.

For the Webmaster and online marketer, Google offers a glimpse into the effectiveness of any site’s networking, and the status it enjoys among its peers.

Last time in July when Google PR update takes place many webmaster ends up with the results that they were not expecting:

Darren from Problogger quoted:

"I went down from 7 to 6 on one of mine"

Blog Herald Webmaster said:

"The Blog Herald returns to PR 7, and the 4 other blogs on the Web log Empire network launched in June have gone to PR 6."

Admin of Pakimp3.org told: 

"My PR went from 4 to 3 as I dint spend much time link building might be the reason for it"

What was your experience with last update, what are you expecting with this update. Anyone want to share their experience? Let us know in the comments.