Several months ago, MacRumors noticed that Apple was using two different suppliers for the Solid State Drives (SSDs) in its MacBook Air models -- Samsung and Toshiba. At the time Samsung SSDs benchmarked significantly faster (both in read and write speeds) than the Toshiba SSDs.
Users reported receiving both Samsung and the Toshiba SSDs in the 2G MacBook Airs making it a seemingly random decision, most likely based on inventory available at time of manufacture.
History has a way of repeating itself and the same situation was discovered by TLDToday in Apple's just-released MacBook Air (Mid 2011). Apple's apparently using both Samsung and Toshiba SSDs in the new Airs and the Sammy modules have been benchmarking significantly faster than the lowly Toshiba sticks.
The 128GB Samsung SSD in his 11-inch Air was able to achieve 246 MB/s write and 264 MB/s read speeds. When he switched to the 13-inch model, however, speeds dropped to 156 MB/s and 208 MB/s, respectively, using that notebook's 128GB Toshiba SSD.
You can check which SSD module you have by going to About this Mac > More info... > System Report... (the new name for System Profiler) and clicking on Hardware > Serial-ATA in the left pane. If the enter for APPLE SSD is followed by SM, you have the Samsung, if it's followed by TS you have the Toshiba module.
I checked my new MBA13/CTO i7 and (luckily) got the faster Samsung module as denoted by "SM256C" in my System Report.
If you have a new, third-generation MacBook Air, please check your SSD and note it in the TalkBack below. Please also note your configuration, specifically if you have an 11, or 13-inch model and your RAM, SSD configuration. If you ordered a CTO model with the Core i7 please note that as well.