In a thread over at the Google webmaster help group Matt Cutts has made some comments that pretty much put an end to using sponsored themes as a linkbuilding practice.
Some people have been aware that this tactic is classed as “buying links” for a while now but the practice is still going on. The worst offenders are using keyword rich anchor text while other people just do it for general link juice. In the second case a penalty is unlikely but in the first case I expect Google might take a dim view.
Here are some of the key comments Matt made in response to a webmaster who had been using this method and saw their rankings drop by 60 places:
ShyBoy, have you been collecting backlinks in any unusual ways? It looks like you may have, and I would pay special attention to that. For example, if you had been attempting to get PageRank via paid links on various templates, then when that PageRank stops flowing (e.g. if Google improves its detection in various ways), the fact that you have less PageRank can also mean that a site won’t rank as well.
The recommendation from your SEO guy led you directly into a pretty high- risk area; I doubt you really want pages like f**kingfilthy.com having sponsored links to your furniture site anyway. It’s definitely possible to extricate your site, but I would make an effort to contact the sites with your sponsored links and request that they remove the links, and then do a reconsideration request.
The issue here is one of scale – if the site had 100,000 natural links and added a few thousand using this method I doubt Google would even notice. However if a large amount of your links are either low quality or ones Google doesn’t approve of then it’s only a matter of time before something goes wrong.