The article "Elements of E-Style" on pages 48 and 50 of the April 16 issue of The New Yorker reviews a new book Send: The Essential Guide to Email for Office and Home which offers a system of proper usage and protocol. The review states in part
"...The authors, astonishingly, come out in favor of exclamation points ('Thanks!!!!' is way friendlier than 'Thanks', ..."
I immediately thought of the rants which appeared in this forum on the subject of exclamation points.