How to increase Page Rank?

I think the point here is that we have suggested PR is not a good measure to use to gauge a sites authority, as its at any point, 90 - 120 days out of date.

So, who is to say that your pr6 site today isn't in reality a pr1 after being bashed by panda et al and vise-versa?

There are simply better, more regularly updated measures to look into. And focusing on PR has been shown to do nothing for your actual rankings, which is why you can see a PR1 site in 1st place, and a pr5 on the 3rd page (assuming those measures are up to date!). Its just too uncertain to bother focusing your efforts on.

Totally agree, it is very important to remember that PR is constantly fluctuating and we will probably never see a truly upto date representation.

When building links I actually tend to focus ont he authority of the domain as a whole using manual analysis and SEOMoz' Domain Authority.

This question has many answers. Google always changes its algorithm so its hard to predict the only way to increase your page rank but instead there are many ways which you have to try each and every time to check with ranks it you are currently performing with backlinks and you find that there is an increase in your rank then go with it else you can do link building and so on.

Increasing PR is a slow process but if you continuously update your site with great content, guest post on relevant sites, share your content via social media and use other white hat SEO techniques while avoiding black hat techniques like keyword stuffing, you will be on your way.

It does take some time, however, like any good SEO company will tell you - sometimes more than a year - to get to page one.

I agree that increasing the PR is a slow process, but that's how natural processes are ... slow. Getting rich quick schemes are unnatural and we all know that ... by now ... I hope.
I think that is consistent with everything that comes out of Google. They want less SEO and more natural growth, with content that is not put out there for the sake of SEO, but because it matters. Content for people, not for search engines.
Personally I think this is a great thing, otherwise we'll end up with the whole of the Internet being one big rubbish dump of cheap content that adds no value whatsoever.
SEO in my view should be more about optimizing existing content, exposure, brand awareness in the context of the natural marketing that companies do. It should not be something done in isolation, content for SEO and so one. PR should be a lagging indicator of how well you've done so far, and in that context ... it's fine to use it.
I hope Google have penguins, pandas, tigers and plenty more other animals to keep our Internet sane and safe.