With useful tools such as the free Disk Speed Test found in the Mac App Store, one could easily benchmark his or hers hard drive and SSD. As it turns out, Apple is still using two different models of SSDs in the MacBook Air from Samsung and Toshiba. It is reported that all Toshiba SSDs found in any 2010 and 2011 model, 11" and 13" MacBook Air, are slower than the Samsung SSDs Apple is using. Before your heart sinks to the bottom of your stomach, check to see which SSD model you've got inside your MacBook Air by going to your About This Mac - System Report or More Info under Snow Leopard - Serial ATA. If you see the Toshiba TS128C SSD model then you've got the slower SSD that's able to perform read and writes speeds generally below 200Mbps. If you're lucky, you'll find that you've got the faster Samsung SM128C SSD.
The difference in speeds may not necessarily mean that you will notice a significant difference in your day to day usage, but if it does bother you then you should try to get a replacement.