So I just got a Macbook and this Time machine looks like a good feature in case you accidentally do something stupid. I want to back up to an External HD but its a laptop and i dont plan bringing my external HD with me everywhere. So can Mac back up each time it's plugged in and then if I loose something I plug it in and go to time machine orrr? Just looking for some details on options I have here. Not really interested in backing up to a .Mac account or buying new hardware, such a a time capsule (which would be nice for time machine but once again only really would serve me a purpose when my laptop is at my house)