So, I just picked up my first mac today at my local apple store (15" MBP - Base model) and I was just wondering, what is taking up so much space on the HD? The capacity is 111GB but only about 75GB was available when I booted up the machine. After transferring my music library (about 20GB) I'm left with only 54GB of free space. This has me a little worried/confused, so what's the deal here? Thanks!