As expected from AnandTech, there is an in-depth review of the new MacBook Air 11" and 13" 2012. They have been testing all models with previous ones, but also checking the differences and impact on performance between the new units featuring different BTO.
So, for SSD, it can be a Toshiba or a Samsung unit, and it can have a impact on the writing speed. If Toshiba SSD are faster for reading and writing compressed data, the Samsung units are superior for writing large files (up to twice faster). In addition, if you are using Filevault 2, you might prefer to have a Samsung unit, so you would have to choose the 256 or 512 GB SSD BTO to try to ensure you will have a unit from the Korean manufacturer.
In summary performance as well as battery lifetime are significantly improved when compared to the previous generation of MBA.
By linathael, original by Lionel