So I just bought an external drive to back off my stuff on my new Macbook (250 GB). I understand that I can partition the external drive (500 GB) so that I can use it for Time machine and to store other files. Okay, so my questions are: 1. With my 250 GB Macbook, anyone have any recommendations on how much space should be alotted to Time Machine? I assume it should be more than 250, but I don't really want to use a lot of space for this. 2. If I decide to use a certain amount, let's say 300GB for Time Machine ,is there some way to change that in the future? Or is it set permanently? Thanks!