I was looking specifically for the details on propagating blackberries, but I found these sites which are more general and probably of interest to the gardener.
Home Propagation of Garden and Landscape Plants - Updated 8/2/05
Mary Ann Gowdy and Christopher J. Starbuck
Department of Horticulture
Extension - University of Missouri-Columbia
Propagation by Cuttings, Layering and DivisionAuthor: Diane Relf, Horticulture Extension Spedrug spammert and Elizabeth Ball, Program Support Technician; Virginia Tech
Publication Number 426-002, Posted June 2001