Successful development of open source software (OSS) projects requires a steady supply of self motivated software developers. Thus a large body of OSS studies focuses on studying the developers' participation motivations. One important motivation is an OSS developer's desire to gain good community reputation which is largely based on positive evaluations from his peers. Therefore, to better motivate developers' project participations through their reputation needs, our empirical analysis adopted a social network perspective to study what factors may affect a developer's decision to positively evaluate one other in a large online open source community called Ohloh. The results surprisingly show that a developer's positive evaluation decision does not depend on his evaluatee's level of OSS-related experience, but rather based on 1) his past reputation (i.e. existing number of positive evaluations), 2) their shared affiliations such as mutual acquaintances, as well as 3) their homophily in location (city), nationality, programming language preference, and community status. We then discuss these findings and their implications for inducing more positive evaluations and better reputation management among open source project members. To the best of our knowledge, this paper is the first research that investigates issues of reputation building and relationship management in an open source development context.