I guess if the object is available for everyone to order, the names of people who ordered it should be available to all as well. If there are privacy concerns, maybe put the number of orders on the public page, and only the owner of the object can see the names. But really, I think the more open it is, the better for the community.
For the comments, on the gallery or my designs page it could simply be placed at the bottom:
[ Picture ]
Trackball Assembly
Date: 19 Oct 2008
Rating
X X X X x )(4)
Comments: 2 (1 New!)
I have 6 pages of objects on my designs page, so clicking through each one to see if I got any new comments would be annoying. If you are familiar with flickr.com, they display a list of recent activity when you log in.
It could be as simple as putting something like this:
(10/19)
*
Joris commented on
Trackball Assembly
*
andre.bois commented on
Mama Ghost
with the user name and object name linked to the respective pages, between "My Designs" and "My Favorites"