Other Authors or Systems that David Allen Endorses

Just wondering if there are some other productivity gurus out there that David feels compliments his system or goes places his does not.

i.e. has anyone read or experienced "Organization from the Inside Out" by Julie Morgenstern? I want to go further in terms of storage, shelving, hanging hooks etc. all throughout my house and am going to read this book. Anyone have any thoughts or opinions on this?

Thanks,

Clark

I'm not sure what other systems DA endorses besides his own, but I've always thought that Mihaly Csikszentmihalyi's work Flow: The Psychology of Optimal Experience is very much in line with DA's system. Csikszentmihalyi's "flow" seems very close to DA's "mind like water".