I have the regular assortment of (multiple) generations of NAS devices at home and in the office as well. But, when you want to go throw that Windows 7 image onto VMware and use it for a few days, or you want to do some editting of your family vacation photos, or you happen to be on a business trip to brazil, it's _really_ nice to be able to just pop a USB/SSD into your laptop and edit/view a way. I sync back to my external drive/NAS when I get back into the office/home.

For those of us who travel for extended periods of time, USB/SSD Flash Drives are a nice alternative to external Hard Drives and/or spending a fortune on Internal Drives w/Apple