We are using AD as our LDAP server (Windows 2008)
According to MS KB: http://support.microsoft.com/kb/2009267
Hardcoded LDAP limitations have been introduced in Windows Server 2008 R2 and Windows Server 2008 to prevent overloading the domain controller. These limits overwrite the LDAP policy setting when the policy value should be higher.
Could it handle our 200,000 accounts?