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You wan't to get all of the links from stumbleupon to your site? You could search this in Google

inurl:stumbleupon.com "yoururl.com"

You change the stumbleupon.com to any domain you'd like to search for links to your site

The theory is that the "link juice" would flow like this:

Private Blogs -> Article -> website

It can be very effective to do this if the links are valuable - some people choose to do it for safety purposes, they believe that their website will not get put into Google's "sandbox" this way, in case too many links were made and various other reasons. For example, rather than create 1,000 links to the URL, make an article and then point 1,000 links to that article which would flow some of the power to the site.

Not all of the power will be passed through to the main website, but depending on the linking methodologies some people have very good success doing this. There are really many variables here, but if done correctly I would say yes indirect links can be very beneficial.

Those blogs do not sound very worthwhile - if the person is adding content and building links to the blogs, they would be much more beneficial. Google has updated their algorithm's and they are beginning to really weed out these low quality sites. At the end of the day, all you can come to is well educated speculation on the matter. If the website is very valuable it may be valuable to build the links indirectly while focusing on very high quality links only to the main website. If the site already has many links and is a decent age, the person may consider building a greater number of links to the actual URL.