Gathering Simple Federation Use Cases

I was chatting to tantek on indieweb IRC and we both agreed that the SWAT0
use case was not an ideal test for the federated social web.  My personal
feeling was that it was a bit much to take on, and complex

That got me thinking as to what concrete tests we could use to test for
federation.

My idea was *friending*, but tantek said that friending was not very high
on his priority list.  Others have said that friending is not important.  I
do think at least this use case could be used to test federation.

I was wondering if anyone was interested in simple use cases that we could
use to try and either

1) join social network functionality together
2) identify what fixes are needed
3) identify which systems allow which functionality across boundaries