Hi, My MBP has 120GB (well actually 111.47 GB according to finder) of which I am currently using 53.54GB. This number fluctuates of course as I work. During peak work periods I can get as little as 30GB free ( I usually burn projects on DVDs when I am done to recover HDD space) So considering this, how big of a hard drive should I get for Time Machine? I was considering getting a compact 120GB to carry with me. This should cover the content of my harddrive but I dont know how much more space those incremental back ups will take up. So how big should the extrenal drive be compared to the mac's hdd?