Apple hasn't marketed as such, as least not in this neck of the woods, but Thunderbolt is clearly a Docking port. The first one ever on a MacBook!! (That I know of)
Take a look at their new Thunderbolt display. With one cable connection, your MacBook gets network, sound, firewire, USB and power(!), all via your external Display. No need to attach a second cable.
Considering that Thunderbolt already is a DisplayPort connection, I don't see the benefit of connection a second graphics card over the PCI-e connection. Some says to have a more powerfull card, over 4x PCIs 2.0?, for games. However lots of suppliers have hard PCexpress (also on MacBooks) GFX cards, but none work with Macs because Apple wont play fair with regards to GFX drivers in OS X.
In the end, to be honest, I find it far more exciting that I can finally replace the 8 cables that I have to plug into my MacBook with just one.