Consider that if you've got a laptop, you're already constantly transporting a hard drive back and forth all over town.
I think the answer depends on whether your are referring to a USB drive enclosure (which is pretty much just a empty shell into which you install a regular hard drive) or a self-contained USB drive that isn't intended to be opened up (I've got a LaCie like this) If it's an enclosure, then as tredegar mentioned you can remove/replace the drive as needed.
In any case, treat your equipment with care, and be sure to unplug/power down the USB drive before you start moving it, but otherwise USB drives are intended to be mobile.