Google Docs lets you select a color for each of your folders, a feature that has been previously available in Gmail. The color will be used to represent a folder in the sidebar and in the document list, so you can easily spot related documents.
Another new feature, this time available only for documents and presentations, empowers you to change the owner of a document. Unlike simple collaborators, the owner of a document can delete it and can restrict the access to a document for some collaborators. This page explains the difference between viewers, collaborators and owner. To become a collaborator and transfer the ownership of some of your documents, select them from Google Docs homepage and choose More actions > Changer Owner.
Judging from the source code, Google Docs will include an option to add collaborators with limited rights - they won't be able to download a document, change its settings, share it or publish it. Creating user groups with custom permissions could be an even better idea.