In reply to Cog:
I have Aperture and I don't really rate it. I bought it for a one-stop program for all processing, including family album and guidebook-work raw photos, but I have gone back to Bridge/Photoshop for work, and I find it pretty frustrating as an iPhoto replacement.
It does save multiple edit versions, as you mention in your OP, but then so does iPhoto - just select 'revert to original' and you can go back to the original version.
The photo import in Aperture is terrible and it doesn't offer any Raw convert options. Also, I don't like the fact that it keep duplicate copies of photos you edit so that when you try and browse a project, it shows you all the edit duplicates - keep the duplicates by all means, but don't display them all the time. There may be an option to stop it doing this but I haven't found it.
My suspicion is that Lightroom is a much better program, but Bridge/Photoshop is probably the best of the lot.
Alan