Just why have financial institutions been so slow to harness the power of social media to boost their reputations? Fear about losing control over their corporate image may be holding them back, communication experts say.

Every week, German engineering conglomerate Siemens posts a short film on its website. Eschewing the usual marketing spiel, the documentaries explore the impact of technology on people's lives. The films are just one element of its social media strategy, which won the firm the top spot in the 2011 FT Bowen Craggs & Co Corporate Web Effectiveness Index.