When creating or editing an album, you have the option to add friends as contributors who can now add photos. It’s perfect for group events so everyone can upload to one single, canonical album, and plenty of other uses.
For example: I just created an album for a recently Door County family trip using Aperture that was set to “Only Me.” Then I went to Facebook.com and added the five other adults as contributors, so now only we can see it, but all six of us can add photos to it.
This is exactly what I’ve wanted for years, and it’s great.