Graham,

I’m of the mind that you’re better off with your photos in one place. As soon as you try to use more than one photo management tool, you’re going to end up with confusion, duplication, or at the worst, missing photos. I say, stick with Aperture, and if you need a feature in iPhoto (like calendar printing), then you can actually access the Aperture library from within iPhoto for exactly that purpose. It’s under the File menu.

The reason you end up with duplicates in Aperture after an iPhoto import is because of the way that iPhoto handles versions. In Aperture, there’s a master file (the original), and any adjustments are stored as metadata, and there’s never an actual file created with those adjustments until you export a picture. And once you’ve done whatever you’re going to do with the exported file, you can delete it. The master and the adjustment instructions are always still inside of Aperture.

In iPhoto however, there’s an original file, and a version. The version changes as you make changes to the image, and if you want to go back to the original (revert), you can. But you always have two versions of every photo.

When you import iPhoto to Aperture, you get both of those. They will get keywords to identify them; I think it’s “iPhoto Original” on the original file.

Ideally, you would have them stacked; the adjusted one on top, the original underneath. I haven’t done an import in a while so can’t confirm how it actually works. I really hope it does work that way, come to think of it :)

How do you get around it? You could always just delete the non-originals, and re-do your adjustments as needed. But that could be a lot of work.

Or just leave it be.

I hope that helps at least a little bit.