Macworld recently took a look at the newest MacBook Air models that were introduced at WWDC. The MacBook Air received processor speed bumps as well as a dramatic $300-$700 price drop. Despite the clock speed increase, Macworld found that the new MacBook Airs were actually slower than their predecessors:
What's weird about the new high-end MacBook Air model is that although it cost dramatically less than its immediate predecessor, it was also slower than that model. The late-2008 1.86GHz MacBook Air was faster than the new top-of-the-line model in 11 of our 18 tests, and as a result, the old system's final Speedmark score was slightly higher. The low-end 1.86GHz model did a better job versus its predecessor, besting it on most tests and improving on its Speedmark score.
They speculate that it could, in part, be due to aggressive thermal management in the higher speed models, but don't have a definitive answer.
The conclusion, however, remains the same as it always has for the MacBook Air. According to Macworld, "if the Air always struck you as being overpriced and underpowered, these aren't the laptops you're looking for.".... "But if the specs that matter most to you are light weight and small size, the MacBook Air is the system for you."