best estimate 80+ gigs, mainly full albums and high quality (mostly 192 variable bit rates), also they are legal owned (back ups of cd's I have or have once bought, but has since been either stolen or damaged)
Last count I have about 2500 cd's, also the best way to not get caught, especially if you have a lot of mp3's is to not share with other people.  Its one thing to help out a friend, or share a couple, its quite another to have your whole drive of mp3's shared to the world.
and yes, removable hard drives are your friends.