I made some changes to ECSD Wireless on April 6th in order to better support high density environments. Shortly after that we had a some issues with Spring 2011 iMacs running 10.6.7 or 10.6.8 not pulling DHCP addresses. It seemed to be confined to one location and that subset of systems. However this week we discovered another location and an apparently larger number of systems with the same issue. In both cases, I added an alternative wireless network and the affected machines started working. I'm trying to pin down exactly which changes cause the problem. In the meantime, if you have or see this condition, please contact me.