What You Should Watch Out For!
Generally, once AD has been configured and set up properly, there is little else you need to do (except, of course, to perform regular checks, as you do with any database). However, the following list describes some of the problems you may encounter with AD, and sometimes these aren't revealed until you write some code to get into AD.
What you should watch out for:
Permissions: If the user your code is running under doesn't have access to certain parts of AD, you will get errors such as "The Server is unwilling to process the request".
Domain format: If you specify an incorrect domain name in your query string, you will get an error such as "Table does not exist". I have found that the dot (.) notation generally works better than the DC DC= format (that is, use root.mydomain.com rather than DC=root,DC=mydomain,DC=com.
Connectivity: Sometimes, you have a piece of code that works very well; and then without making a change, it doesn't work anymore! Other than calling Mulder and Scully, it generally means that if your PC has a dynamically assigned IP address, you need to renew it. Sometimes, for an unknown reason, multiple GC/LDAP queries cause Windows 2000 to lose its IP address, and so cannot see the AD server(s) anymore.
Replication: If the GC is not replicating around the forest correctly, you will find that you will get incorrect results, or you won't be able to even query the GC at all.
DNS: AD totally relies on DNS. If this isn't right, you've got problems!