If those adaptors are available. I already use a USB ethernet adaptor with my MBA and it's terrible since it only does Ethernet 100 mega bits as opposed to giabit Ethernet. Also, because it's USB it uses a fair amount of your CPU.
The other adaptor that does offer full gigabit Ethernet via Thunderbolt happens to be attached to a 27" screen and costs $999 so it's not really a convient solution for everyone.
Sure, the Belkin Thunderbolt thing does promise this connectivity, but when will it actually come out?
I have the Apple USB adaptor and the Belkin Gigabit USB adaptor. (http://www.belkin.com/IWCatProductPage.process?Product_Id=281799)
The Belkin version is at least 50% faster than the Apple version. Both use USB2 as the source (obviously).
Belkin ~ 18MBps
Apple ~ 12MBps
"Real" Gigabit ~ 100MBps - so still a way to go.
Belkin Thunderbolt thingy ~ always at least 9 months away from launch !