They report that much of the MacBook Air's external design will not change; however, the internals will receive a significant revision.
The current MacBook Air is powered by a custom Intel Core 2 Duo processor with a lower voltage process to conserve power. The new MacBook Air however, will trade that CPU out for a standard Penryn-class Core 2 Duo. And, as such, the CPU will be able to dramatically increase, from 2.0 GHz and potentially beyond. As such however, power drain will increase. Apple will curb that constraint with a higher-capacity battery. However, we can confirm that the new MacBook Air will require a 60W power adapter to fully charge, much like the current MacBook family.
PhoneNews expects that the MacBook Air internals will be more in-line with the current MacBook internals. They also expect the hard drive will be upgraded to 120 GB, and optionally 160 GB. SSD prices should remain at around current prices.