TLDtoday has discovered that there is a sizable difference between the read and write speeds of the new 2011 MacBook Airs. This variance is attributed to the different SSD suppliers that Apple is using. Benchmarks show that write and read speeds for Samsung drives are anywhere from 60-100 Mbps faster than Toshiba. TLD notes that 13″ Airs generally have the slower model SSD, while the 11″ houses the speedier Samsung drive.
To check which model your Air is carrying, go to the “Serial-ATA” tab in System Report; TS in the model name denotes a Toshiba drive and SM is Samsung. There is no way to tell which version a MacBook has without booting it up, so be wary when buying.