Does is make sense to use Time Machine with a Macbook pro? (I use it with my imac and love it...) I got my wife a hard drive 320 gig to use with her Macbook Pro, but she'd probably only plug it in on some nights during the week, and most weekends. Will unplugging it and plugging it back in all the time make for a confusing operation with Time Machine, or would that still be a good way to use Time Machine for backing up her macbook pro? thanks!