Something that doesn't seem to have been mentioned explicitly is that DHCP has to be turned off on all access points/wireless routers. There must be only one central DHCP server for the entire network.
But as mentioned, this is part of the spec. I only realised the same thing last year though, so it was nice to be able to remove my 4 different SSIDs from my home network and just use one.
The only down side is that it isn't obvious which AP is in use by any particular device (g or n) or if any AP has died. But unless it causes noticeable problems I don't really care.