If you are using Sun Directory Server 5.2, please note that you can't use ldap_rename to move an entry. According to Sun's own documentation: "[...] At this point in time, Directory Server does not support the ability to use the modify DN operation to move an entry from one location in the directory tree to another location." (http://docs.sun.com/source/817-6707/resultcodes.html)
The problem is that php does not return any error and the operation seems to complete succesfully, except for the fact that nothing really happens. If you check the server logs, there will be an "error 53" entry (server is unwilling to perform).
hope this saves someone's couple of hours nasty searching...