I think I'm in the same anal league (oher misses) as JPM and Keefer.
My bikes cleaned weekly, as thats about as often as I ride it...but for no other reason than I like my bike to look mint, and I do actually enjoy doing it...Hot and soapy water followed by Muck-off. Autosol for polishing and Autoglym for palstics. Once you get on top of it its a 20 miute job anyway.
Even the DR350 gets cleaned on a regular basis.