This is all very good info, except I think Macs are way overpriced and unnecessary unless you like shiny objects.
I'd recommend taking a look at the circulars for Best Buy, Circuit City, Staples, etc. - then call and make sure they have it in stock before you go.
Also .. (personal opinion here) make sure it has a SATA port, and HDMI. I think more and more devices will be using those over the years, and SATA is much faster than USB for backups.
laptops have external SATA and HDMI nowadays? wow, that's pretty cool. those can't be very common though, right?
i've seen it on a few. maybe not on the majority of models, but if you're going to make an investment now, it's definitely worth it to pay a few dollars more for those connectors. I think HDMI is cool because it carries sound too (pretty sure it does on a laptop, anyway)