It seems that there are a lot of people discussing and making backlinks without fully understanding PageRank.
Let’s dissect the issue:
Page Rank is NOT website rank. It must be known that Google, and all search engines for that matter, do not index or look at websites, they look at webpages. Likewise, Google assigns PAGE Rank to pages based on the overall authority that a page has based on their page rank algorithm. It is just one of over 200 variables that go into deciding a pages ranking in the SERPs, and is not essential to rank well for a competitive term.. To elaborate further, establishing authority and attaining a high search engine PageRank does not mean you will have high rankings in the results pages.
A great technique for getting SEO benefits out of an irrelevant high PR backlink is to point it to a relevant backlink. Remember, if you can use anchor text, then you have a relevant link on your hands. This strategy is for when you cannot use anchor text. How far you want to take this strategy is up to you, but the idea is quite simple. If you really want to get the most out of a high PR backlink that isn’t yet relevant, you can create the link to lead to any backlink with the proper anchor text, and that is preferably, surrounded by relevant content. Example:
High PR Link -> Relevant Link w/ Anchor Text -> Your Site.
Link building like this can be very beneficial to your site, but only if you're understanding PageRank and how it works.
The reason why the above scenario isn't quite ideal is that you lose 10-15% of the PR being passed on for every step along the way. Your high irrelevant PR link will send its respective PR to your page with your relevant link. Your relevant link will then pass this link juice minus 10-15% to your site. Also, the PR that leaves a page is divided by the number of outbound links on the page, so when your high PR link gets to the page with your relevant link, that "link juice" will be divided by the # of links on that page and sent through those links minus 10-15% (except for nofollow). Understanding PageRank and its flow is essential to crafting an effective backlinking strategy.
So should I hoard my PR? Find out why PageRank sculpting probably isn't a good idea: Pagerank Sculpting