Id like to point out...
It has 4 ports: Magsafe (AC), Headphone, USB and a Mini DVI port that can be broken out to Composite, Digital and S-Video as I recall. The latter three 'drop down' when needed- thats why they are hard to discern in the product shots.
As someone pointed out, I am sure that a bevy of port replicators will be released, this is the first Mac I know that opens the door for enterprising developers to write the drivers for the many existing options too.
Lastly the MBAir is not limited to borrowing optical drives from nearby Macs, it can wirelessly possess PC hosts too. :)