A tip which may be useful: I do not put everything into Aperture at all. I download from the memory card to a folder on the desktop and then I use Photo Mechanic to do a review of the images, culling them out there before I ever take anything into Aperture. Only after I've done this do I then import the images I'm likely to work on into Aperture. This saves space in my Aperture library, quite a bit, actually.