http://www.seomoz.org/blog/10-illust...ation-of-links
Although it's from last year, this is a pretty good article on the value of different types of back links.
At one point it says:
"Papers like Microsoft's VIPS (Vision Based Page Segmentation), Google's Document Ranking Based on Semantic Distance, and the recent Reasonable Surfer stuff all suggest that
valuing links from content more highly than those in sidebars or footers can have net positive impacts on avoiding spam and manipulation. As webmasters and SEOs, we can certainly attest to the fact that a lot of paid links exist in these sections of sites and that getting non-natural links from inside content is much more difficult."
It appears that Search Engines don't value links in footers and sidebars as much as they used to.
In another part of that article it talks about links from multiple pages on a domain and says that they do not help you any more than just one link. Hence, links on blogs in their blogroll where the link appears on every page on the blog will not help you any more than just one link. IMHO having a link on every page on a site, using the exact same anchor text, can actually hurt both sites...the one that the link is on and the site that the link points to.