I was just wondering about that, too. Had to change only the first image of a product, to be able to do that I first have to remove ALL images, then add them all over again. That should not be necessary I think. And all the images are uploaded again.
In my opninion three features would make this MUCH easier to do:
1. possibility to change the order of the product images
2. possibility to change the source of the images (if you click the edit button there's nothing to edit besides the name of the image, would be helpfull if you could select/upload a new image)
3. a media-manager, so you can re-use uploaded images already.
This is not something that's easy to explain to my clients, things like this mean that it is NOT an easy shop to be managed by themselves (and really, that is what clients ask for). I can imagine what happens if they want to change just one pic by themselves: do it over and over and over again, with a lot of images being uploaded over and over again, wasting a lot of diskspace and growing frustration.
Would be really great to see this in the future (if only the first two features could be realized it would already help some). Hopefully you have the time to look into to this.
Thanks!