Yes, they degrade over time, but they are still faster than hard drives.
Anyway, Digilloyd did a test recently on the 512GB Toshiba SSD that Apple uses in the MacBook Pro. It ought to perform similarly to the Toshiba SSD in th new Air. The drive is slower than an OWC drive, but it does hold up reasonably well to severe usage.
http://macperformanceguide.com/SSD-RealWorld-BeforeAfter-AppleToshiba512.html