I've seen lots of comment on Aperture, but this is first one to show how important stacks are. This is a feature that drew me in the first place and now using it daily, I love it. Very simple and very powerful.

My tuppence worth of requested change: I'd like a 'merge keywords' feature, recognising that most of us come with a huge library of images that is running under one or more previous apps (like iPhoto) and each app has its own keywords.