The user-generated podcasting service over mobile opportunistic networks can facilitate the user generated content dissemination while humans are on the move. However, in such a distributed and dynamic network environment, the design of efficient content forwarding and cache management schemes are challenging due to the lack of global podcast channel popularity information at each individual node. We design a distributed reputation system at each node for estimating the global channel popularity information which is significant for forwarding and cache management decision. Our simulation result shows that, compare to history-based rank scheme, our reputation system can significantly improve system performance under community-based random way-point (C-RWP) mobility model and localized channel popularity distribution.