This isn't new and it isn't a breakthrough, I just need a doc that shows people how to share a bucket with someone else. It turns out this is a very important feature when bootstrapping a blogging system where your content isn't in someone else's silo (otherwise known as silo-free blogging). It turns out it's pretty easy, and credit for realizing how important this is goes to Joe Moreno of Adjix. 

You're going to share a bucket with me. This will mean that I will be able to store stuff in your bucket. For this experiment I'll just post a picture there. Once you get the picture you can take my name off your bucket.  

1. Log into Amazon's AWS portal, click on the S3 tab.  

2. Click on one of your buckets, in the left column. 

3. Click the Properties button. 

4. In the bottom panel, click on Add more permissions, then enter the long id below in Grantee, check Upload/Delete and click Save. Screen shot. If you're not sure what you're doing, you can skip this whole deal. Be careful about granting permissions to buckets.  

5. Post a comment here with the name of your bucket. (Assuming comments are still enabled, I'll disable them after the experiment is over.)