Good KM tools facilitate

EEK Speaks on "Low-Focus Thought" in Knowledge Management Systems

Good KnowledgeManagement tools facilitates the discovery of these weak connections, and make us less reliant on luck. Blogging is great, because it encourages people to link, which encourages bloggers to search through old entries -- both of others and their own. This is an example of tools facilitating a pattern, and it's one reason why blogs are a powerful KnowledgeManagement tool.

This seems an excellent description of what KM tools are supposed to do - help us make these weak connections and bring them to the fore. Rather than relying on serendipity (as Seb comments), use tools and processes that ensure that you return to your own stored knowledge. You are bound to see something new in those old reports, papers and discussions.