We tried this for awhile, but it did not show for back links, nor, much human traffic. However, our company is business service oriented. So, for back links it is not worth the effort. However, if your company is entertainment oriented, and there is a large community in My Space interested in your product, then certainly, you should explore a My Space campaign. It's not all about "back links" and "SERP". It's about driving qualified traffic to your site.