1) How often does Google Update PR?
1a) Is it the same for all websites or not?
1b) If not, what matters? What are the factors influencing on that?

Here http://www.realestatewebmasters.com/thread18219.html

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Bellingham Real Estate
Bellingham Condos
Bellingham MLS

Google updates page rank on a continuous basis. The toolbar, or as some have come to call it, the foolbar is updated about 3-4 times per year. Just remember that what google shows in the foolbar is generally not everything that google knows about a site, be it page rank or backlinks or whatever. What matters to google is links and staying within their guidelines.

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Mack Perry - Atlanta Georgia Real Estate, Atlanta Homes for Sale and the Atlanta Real Estate Blog