I've just done my IUWVN class this week and one slide in the course docu was about the AP deployment.
Cisco recommends to put not more then 16 APs in the same subnet/VLAN together with the WLC managment interface.
So if you've more APs you should put it in a dedicated VLAN but with a max. of 80-100 APs.
That would result in a lot of different AP VLANs in a big deployment.
Anyone has more infos/documents/links as I'm not able to find anything about this "best practice" on the Cisco homepage... or how are you doing it in your deployment, do you follow this recommendations !?