I don't remember any study with a comparison of two subjects, but I know this one with a comparison of 4: Thomson, L. (2012). PIM in the Professional Home Office: An Ethnographic Study. Workshop on Personal Information Management (PIM) 2012 at ACM Conference for Computer Supported Collaborative Work (CSCW), Seattle, WA. http://pimworkshop.org/2012/pdf/thomson_2012_pim.pdf