I am talking to a few museums and archives and several of them are interested in considering Commons for their collection. At the same time they are also considering Flickr.

The issue they have with Commons is its restrictions. One of the museums said it like this: "We have done our best to ascertain the copyright status of much of our material. We have not been  able to find the original copyright holder or someone who inherited these rights. When we post our material to Flickr, we just remove the material when a copyright holder turns up and asks us to. Doing it in any other way requires much more effort. Effort that we rather spend in more productive endeavours like digitising and annotating."

My question is, will it be acceptable when a museum or archive provides us with their material and when we learn about a request to take down material, we do this when requested by the copyright holder.  This is not considered an issue with Flickr !!