Here is a link to some info provided by Jonathan Carr from Lyra. I would put the Cardas LP into the degaussing (Cardas refers to the frequency sweeps as degaussing not demagnetizing although the words seem to be interchangeable when used by many people) camp as opposed to more active and direct demagnetizing by things like the "Fluxbuster".
Active demagnetization is a bit controversial with a number of cartridge manufacturers strongly recommending against it and saying it will void their warranties.
http://db.audioasylum.com/cgi/m.mpl?forum=vinyl&n=61192&highlight=degaussing+demagnetizing&r=&session=
