There are so many variables involved in assessing backlink quality and as of recently, the process has become even more complicated. There are some "rule of thumb" points most SEOs consider when analyzing potential backlinks though. For instance: thematic relevance of a website; popularity (the more visitors a prospective linking site gets and the more socially popular it is, the better); website authority (that is composed of domain age, Alexa Rank, etc.). But what other factors? PR, for example? Is it as important as it used to be? Does geography of a prospective backlink matter? Do you build links with relevant websites that are hosted in other countries or you focus on links from the local sites only? Share your experience in evaluating prospective linking sources. What are the factors you usually take into account? And what makes a good backlink in you understanding?