I have been doing this with 10.8.3 since April without any issues (knock on wood).
All I do is type in my domain name, and a unique (to AD) computer name. Then click 'Bind' and put in a valid AD user account that can join computers to the domain.
Are you sure your Mac is in a network that can talk to the AD Domain Controllers?
When you say you can RDP, do you mean from your Mac to the 2k8 R2 server?
I just tried to do a port scan of my 2k8 R2 server using Network Utility and for me to even get a responces I had to disable the firewall for a minute to test this. Weird, I didn't know 2k8 R2 did that .
I can join computers with the firewall on the server turned on though. We have Access Control Lists (ACLs) in our router here to help to manage some of the allowed network to network traffic. Is it possible you have something like that in your environment?
Here is what I get back on the completed scan...
Port Scan has started…
Port Scanning host: 172.20.8.58
Open TCP Port: 53 domain
Open TCP Port: 88 kerberos
Open TCP Port: 135 epmap
Open TCP Port: 139 netbios-ssn
Open TCP Port: 389 ldap
Open TCP Port: 445 microsoft-ds
Open TCP Port: 464 kpasswd
Open TCP Port: 593 http-rpc-epmap
Open TCP Port: 636 ldaps
Open TCP Port: 3268 msft-gc
Open TCP Port: 3269 msft-gc-ssl
Open TCP Port: 3389 ms-wbt-server
Open TCP Port: 5357 wsdapi
Open TCP Port: 47001
Open TCP Port: 49152
Open TCP Port: 49153
Open TCP Port: 49155
Open TCP Port: 49156
Open TCP Port: 49157
Open TCP Port: 49158
Open TCP Port: 52081
Open TCP Port: 52089
Open TCP Port: 52101
Open TCP Port: 52137
Open TCP Port: 52138
Port Scan has completed…
