We are using 3750E's and 4500R model switches on our perimeter with DHCP snooping enabled. We have a central DHCP server and all of the switches write their databases off to a central TFTP server.
example: ip dhcp snooping database tftp://<path>
This was working fine until the day we upgraded our domain and dchp server to 2008 active directory. After that, the 3750E's no longer update their database's on the tftp server. The 4500R's however are still working.
show ip dhcp snooping database Agent URL : tftp://<path>