reply to Liberty
Re: [OS X] iTunes folder If you pony up for iTunes Match you don't need to copy over any of it and you can stream whatever you want. Or if you are on the same network you can use Home Sharing in iTunes to access another Mac's library to play content while you are working.
So really you don't need from iTunes if you want to save the space.
I'm in the same boat as you, 13K songs plus tons of movies and videos; a MBA with 120GB...no room for this stuff. So I use iTunes Match and Home Sharing to listen or view any of my content on my MBA.