Haven't heard anyone mention that the page ranks were updated yesterday!!!
Some of my internal pages lost thier rank altogether, while other gained PR for the first time...

My hompage stayed the same.

Did anyone notice any changes with thier website?

Actually it started days ago...

On various datacenters of Google update..

Do you think the changes I have seen to my website are final for now or will more changes happen over a certain time?

Nothing for me. I introduced a couple new landing pages last month, so if anything big happened, they would have gotten some toolbar love.

The term "landing pages" is this something you concentrate your SEO on? I have not idea..

Landing pages are the main home/portal/navigational pages on your site where you hope will be your visitors' first experience with your site (and design them as such) ... aka the first page they see when they land on your site.

I want to ask onething:
Is it true that Land Page gets Ranked easily than other pages. I am very confused about this.
Lets say I have 100 pages, so do I need to build links to all those 100 pages to get Ranked in Google?

Thanks for your time.

The more different pages you have links coming to, the better.

My pagerank for the inner pages keeps changing??? It is very annoying.. Do you only get PR if you have links going to that page?

Yes ... PR is simply a statistic that measures incoming links.

Yeah, PR is affected with incoming links