Airport connection intermittent before logging in

We've got several hundred MacBooks here connecting via Airport to our network and bound to AD and OD. The model of MacBooks range from 2006-era to the most current. Most of the time, we'll have a couple out of 30 (sometimes as much as half) fail to establish a network connection upon boot. They do not have an IP. A restart sometimes fixes it, but sometimes not. Usually, logging into a local account will establish the wireless connection (strong signal) and then we're good to go. Our wired clients do not appear to suffer from this symptom. Has anyone seen this out there or know where we might further look? I've tried with fresh preferences in /Library/Preferences/SystemConfiguration/. Looking at logs, I can't see anything that sticks out. The Airport interface is loaded at the same time on a machine that connects and one that fails. Thanks in advance. EDIT: These are mostly 10.6.4 clients with possibly some 10.5.8 clients. A "factory" OS versus a custom image doesn't seem to impact the behavior.