You are right, ncc, AIX has a lot of users. Moreover, I would say that AIX will have more and more users.Some years ago, the Sun systems were the biggest ones. Now, the AIX systems are the biggest in the world.
So, I think that AIX must be present here. And I think that AIX should have it's own subforum.
Personnally, I would like to see the AIX posts in their own forum, clearly named AIX, instead of being something strange like "Operating Systems > UNIX (Other Flavours)".
@the empty calorie : you are right, AIX supports the PowerPC chips.
More interesting, the new power5 chips support partitionning and sub-partitionning. This means that you can put several OS running at the same time in the same box : the database server, the two application server machines and the three web-server machines.