Well, they don't carry much value since most of the time it won't be a site related to your outbound link. Also, majority of people just remove these links anyways, I find this to be a rather deceptive and useless link building technique. Sweetfunny also mentioned something that Matt Cutts said the other day in a Google group regarding penalities for template link building. I would spend my time building unique quality rich content on my website to build backlinks, it will help get you more "natural relevant" backlinks, think about it why do people even link to a site beyond SEO\Pagerank factor? It's because it's providing useful or entertaining content they want to share. Why do sites like wikipedia or about.com have so many backlinks? Thats right, useful content and people link away to it like crazy. Content is king, backlinks are the 2nd in command.
From http://www.avivadirectory.com/downloadblog/?p=338#more-338 http://www.mattcutts.com/blog/by-the-way-2/ http://weblogtoolscollection.com/archives/2007/04/12/on-sponsored-themes/ Sultanofseo, how many downloads did your theme receive ?