Google crawling your iFramed content will not do anything for your PageRank. It would be great if I could iFrame KimKardashian.com on my website and have all the search traffic on my site. This does not happen, because the HTML source in the site frame does not appear in your html source.
However, I think that with the new Panda algorithm developed by Googles, which will be sophisticated with regard to its concentration in the user interface, it will help your website if you are a popular website with a high content content. This is just an assumption, but Google can follow the link in the iframe src = "link" to a high content site, and then give "dots" to your site to improve the user experience.
I came up with this idea by reading these articles: http://www.entrepreneur.com/blog/223765
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