Answer quickly: What does the new MacBooks Air lack compared to all other Macs today? Yes, because: FireWire 800 and Gigabit Ethernet ports.
But they have Thunderbolt, and that is enough.
What you see above are two adapters that Sonnet Technologies presented during the NAB Show 2011, in April: Allegro and Presto. The first a Thunderbolt adapter for FireWire 800, while the second a Thunderbolt adapter for Gigabit Ethernet.
It is a great alternative for those who are not going to buy one of the new Apple Thunderbolt Displays, which also act as a hub for these and other connections. Their price, when they reach the market, should be much more friendly.
[tip from VR1]