Ah yes, I'll just tell my mom to write an XML-parsing script to move the files around in case she ever changes her setup. ;)
And even Finder quicklook seem to render the full .jpegs just fine and fast enough, so wasting so much disk space on a useless preview/thumbnail feature (to me) is a dealbreaker. I'd even be willing to accept missing or postage stamped thumbnails, rather than having to uninstall applications and remove music to make room for my photos.
And the metadata is stored inside the iPhoto/Aperture library package. For Aperture at least it is an open standard XML file so there is no 'lock in' what so ever.