Andrew,
You need to add subscribers to the tasks. Multiple assigned to is not possible, as far as I know. Subscription works in 2.2.1. Assignement of tasks was found buggy by me in 2.0 - no user would show up. Also subscribers list too was empty. 2.2.1 seems to work fine with this. The only issue that still exists is that once you give a due date, it throws and error if you try to change the due date.
Cheers
CJ