I'm currently taking a lookt at splitting email using gnus. It would be a client side replacement for procmail. The advantage being ALL email downloaded at the server would be ing a single IMAP onbox so its's easier to see ALL from more limited clients, and that the splitting into seperate folders is more easily controlled using regexps on the Gnus client side. Anyway, more to come soon as I just got it working - here's the bookmark page:
And, woohoo, I just got it working so that emails from BBDB entries tagged with gnus-private get stored in special folders as specified by that BBDB field. And all with IMAP. Wonderful stuff once more.