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?

Google updates PR continuously (for all web sites) but only updates the toolbar PR every few months.

If you want to get visitors from ranking in Google, there are better things to concern yourself with than toolbar PR (like anything else). Don't worry about PR, it's a red herring.

Originally Posted by tik_tik

1) How often does Google Update PR?

Toolbar PR which is updated almost every quarter but the actual PR is a continous process

Originally Posted by tik_tik

1a) Is it the same for all websites or not?

No. Its even different for a same page having 2 different URL. Its for every page on the web ranging from 0-10 (there could be exception for pages having no page rank)

Originally Posted by tik_tik

1b) If not, what matters? What are the factors influencing on that?

External and internal links pointing to that page.

I am totally agree with shabbirbhimani, he is saying very right.

get quality backlinks pointing towards ur site with good PR ...

this will bring ur site a good PR too ...

the remaining points of yours are cleared by other members very well

Get backlinks from related and good PR sites! it happens at least 3x a year.

Yep.. It is supposedly 3-4 months interval but it seems like 1 1/2 months to me. From January 10, which is the first google update of this year until last week of February.. I wonder why they've updated so soon.

I have to wait for a quarter again....

Originally Posted by tik_tik

1) How often does Google Update PR?

It's not updated on set-dates. Google doesn't usually broadcast exactly when they will update it, but there are certain websites that claim they know when one's coming.

Originally Posted by tik_tik

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

Generally, there's a Google PR update across the whole web which affects most websites.