Firm-specific, idiosyncratic knowledge is increasingly being recognized as a possible source of competitive advantage in today's business world, where more traditional sources seem to become less effective, to the extent of suggesting new approaches to strategy theory and even to the theory of the firm. This is routinely confirmed by the preliminary results from an on-going study of knowledge management (KM) approaches and practices used in Spanish firms. In this study, several senior management respondents unambiguously consider firm-specific knowledge very important for their firms' competitiveness, although they recognize, not surprisingly, that general purpose knowledge is also needed and in a higher proportion. However, when the specific KM practices used are analysed, it turns out that the majority of them do not seem to be particularly well geared to firm-specific knowledge development and usage, and neither for the effectiveness of the associated learning activities and processes. This suggests what could be a fundamental mismatch between the type of knowledge involved and appropriate KM practices. In this paper we present preliminary evidence stemming from the aforementioned study, make an attempt to characterize the kind of mismatches detected, and suggest ideas for further research on the practical and theoretical implications of the results obtained.