I have a MBA and would to use Aperture via an external HDD. Anyone currently using an external HDD as their primary storage device for photos with or without an MBA? Also, does Aperture work and play well with other photo management software like Picasa. What I mean is will Aperture rearrange/rename/modify the original photos? I don't want to switch from what I use now until I am sure -- thus the need for Aperture to leave my originals as is. I can make a copy of all of some of the photos if need be until I am sure I want to switch to Aperture. Thanks for your input.