Anya and I tried to create a new role in SEAD: Contributor. Our intention was to have a role that allows people to add things and edit their own stuff in a space (and view things) but gives them pretty much no power to edit, delete other people's stuff in the space or publish. You can see how we set up the role in sead2-dev. Here are the issues we found:
The person in the contributor role can't (but should according to the setting):
-the links are missing on the project space page to create/add a dataset
-from a dataset page you;re not allowed to add files to a dataset (the only way you can add is my creating the dataset and then sharing with the space)
-can't add a description to a resource
-can't add a dataset in the space to a collection
(note: all this seems to change for folders in a dataset)

The person in the contributor role CAN (but should NOT according to the setting):
-delete a dataset from the list of datasets on the project space page