The Active Directory plugin is finally usable in 10.5.2, but some environments require workarounds.
1.) Your domain must resolve to the ip address of a domain controller. This was not a requirement in previous versions, but Apple is apparently making it a requirement as they closed my bug stating that it was a configuration issue with Active Directory since creation of a domain sets up this dns info by default. If your domain does not resolve to an ip, you need to fix it, or as a workaround, edit your /etc/hosts file to point the ip of one of your domain controllers.
for example if you know you have a domain controller at 10.3.1.23 and your fully qualified domain is domain.forest.com, you’d add this line to /etc/hosts
2.) Allow Authentication from any domain in forest does not work. Uncheck this box in Directory Utility or using the corresponding flag in dsconfigad. If you don’t do this, the join may succeed, but you won’t be able to lookup or authenticate users or even use dscl on Active Directory. When you uncheck this option, just be sure to add the correct domains to your authentication search path in Search Policy of Directory Utiltity.
3.) Allow Administration by Active Directory Groups does not seem to work. In 10.4, this option seems to nest the AD group you want to allow for administration into the local admin group, so the workaround is to do the same in 10.5 manually using dseditgroup.
sudo dseditgroup -o edit -a “DOMAIN\group name” -t group admin
replacing DOMAIN\group name with your domain and group that you want to give admin access.
This group nesting method gives members of your AD group admin access for both Apple’s Authorization APIs and sudo.
These workarounds got me working, logins are painfully slow, but that may be due to the hosts hack.
Update: Under 10.5.3, most of these problems are resolved. If you are still having slow logins/joins, there are possible workarounds.