Can look like either of these two: http://www.canadavisa.com/canada-immigration-discussion-board/august-2011-applicants-lets-get-the-waiting-game-started-t78342.0.html;msg1216693#msg1216693
http://www.canadavisa.com/canada-immigration-discussion-board/-t41886.0.html;msg1032052#msg1032052
People under Family Class as well as the other streams get it.
First of all, everyone should get AOR, and if you don't without doing anything, they are required to send it to you upon request so just "force" one by emailing them. Yes, you may or may not get an IA letter. As I've said before, Buffalo has a great deal of inconsistency and variance. The IA is not like the AOR because it will typically come via postal mail rather than email and includes information that is very critical for you to know. Let's say your interview will be waived, as chances are it will be. I don't believe they send an IA just to notify someone that their interview was waived (didn't happen to me and never heard of it happening to someone else) but if you are required to submit another document or the RPRF, you will get that information (along with the statement that your interview was waived) in the IA.