I have a form where two Addressfields appear side-by side. They are attached to two different Entity API entities.
I have a special 'Company Address' entity that allows me to capture addresses for companies, for reasons that are too dumb and complicated to go into here.
This form allows you to fill in your 'Registered Address' and 'Invoice Address' at the same time.

The addressfields behave much as they should, however, there is one piece of strangeness; When one changes the country on the second Address field, Ajax changes the required fields, post-code, etc, for the FIRST addressfield. This will almost certainly be something to do with the javascript not being specific enough. Because technically speaking these are both single cardinality fields on two different entities, they'll both have a delta of 0.

It's not a show-stopper for us, but it it's a quick fix, we'd love to know about it! It's causing client angst! ;).