My wife's new iMac needs a backup drive, but I'm not sure which size to go for. I'm getting her a 2.5" external Firewire 800 bus-powered drive, so an unneccesarily large drive is a waste of money in my opinion. (if she ever does need a larger drive I can just pop in a new SATA drive mechanism in the enclosure for her). Currently, she's used around 80 GB of her 250 GB drive. The computer's running 10.5 Leopard, so she'll be using Time Machine (being a Tiger user myself I have no experience with Time Machine, but from what I've heard it works as advertised). She's a "general user" -not into huge audio/visual files etc., so I don't think the drive will fill up too quickly. How big a drive compared to her Mac's internal 250GB drive should she get? Will an equally sized external drive do? I can also get a 320 GB drive, but it costs more of course.