It's obvious that you can get a sitewide (blogwide) link with WP theme sponsorship. But you should not buy 100s of wp theme sponsorships because many sites have got banned/penalized because of this.
I've seen sites get severely penalized from wordpress theme sponsorships. I've personally tested it. Had to beg and plead to get the site re included in the Serps. Do not buy wordpress theme sponsorships!
i have seen some sites getting ranked higher doing so but they also did other forms of link building. i myself tried this method and sponsored few 6-7 months back and yet to see any backlinks. the problem is, lot of people just remove the footer links which is easy to do if not encrypted. others keep changing themes of their sites which is a common practice. if you want to see SOME backlinks, you need to sponsor not one two or three, but MANY themes
Really ? care to show me some proof or post some details of your "testing" ? I am getting backlinks from my free themes for almost 3 years now. I have backlinks on free xhtml/css templates, wordpress themes, drupal themes and I was never penalized. Actually some of my templates ( the simplest one I ever made got me tens of thousands of links ! ) are used on .edu sites and on some pretty high PR. Traffic is good also ! So this bullshit about penalizing is just pure bullshit. Just make sure there are only 2 or 3 links in the footer and not 5 or 6. I saw something talking about Free WP themes sites were penalized or something. That has nothing to do with sponsored links. If you know what you are doing you can get 100 000 backlinks from 30 themes in one year. Of course you cannot expect to WIN if you only have backlinks on WP themes.... I never really bothered with who takes links down. Encrypted footer in some cases is even worse than normal one. This thread reminds me of those who say DP coop is bad for SEO Sure it is bad if you don't know what you are doing....as with everything else in life !
I submit studio7designs.com as an example of why I believe theme purchasing works. If you look at their back links, a great number of their 200,000+ links are from sponsorship of wordpress blogs they probably created (since they are a design agency). They are a PR8 and are #1 in Google for their relevant keywords.