Another example of why I love WordPress. Somebody has built a new theme which, with the help of a few common plugins, becomes a contact manager - with search, tagging, 'related people', etc. But I think it can be pushed further.
Using the standard WordPress comment functionality, I don't see any reason why you couldn't turn this into quite a sophisticated CRM tool, along the lines of 37signals' Highrise. You'd automatically get an RSS feed per 'client', and a global RSS feed for 'all client activity'. Plus, it would all happen on the client page - no need to go 'back end'. Ooh, I'm buzzing with ideas on this one already.