Well I don't really have any experience, at all, with events this large but why should that stop me from taking a stab at it?
1 - Apple should have been the only ones serving up wireless access. It's their event so they should have arranged for wireless access to be provided.
2 - I've heard the Xirrus does well in high-density situations so maybe that is something they should have explored. (not too familiar with Xirrus though)
3 - I don't think I would bother trying to serve up 802.11n. I say stick to a/b/g for an event like this and use any airtime fairness tools you have available to you.
4 - WIPS. This would be essential for enforcing the 'no third party APs' portion of the conference. Three, or more, sensors and you can start trying to triangulate any rogues or unauthorized APs that do pop up.
5 - Use a 3G enabled phone. I'm not saying he shouldn't have used 802.11, though. I'm just saying we alway plan for the worst and a lot of newer APs even have the ability to use a cellular connection when their primary connection goes down. It never hurts to be prepared just in case.
Well, there are my thoughts,