The folks at Macworld ran some formal benchmark tests on both the 11.6-inch and the 13-inch Airs, comparing them to their predecessors and even a 13-inch MacBook Pro. The results may surprise you. To begin, the Speedmark 6.5 score doubled when comparing the 13-inch 1.86GHz MacBook Air and the 2009 13-inch 1.86GHz MacBook Air (Speedmark is Macworld's benchmark test suite). Most of the gains were made over drive-based tests, as the new Air's flash storage was able to show off a bit. Duplicating a 1GB file on the new Air took 13 seconds; compare that to 69 seconds on the model from 2009. Likewise, compressing a 2GB folder was 21% faster on the new Air.
Other benefits include graphics improvements, despite the new Air's integrated subsystem. The nVidia GeForce 320M in the current Air produced over 3 times as many frames per second while running Call of Duty 4 when compared to the nVidia GeForce 9400M that's in the 2009 MacBook Air.
Processor-intensive tasks were also better on the current Air and the 13-inch model even out performed a 13-inch MacBook Pro when it came to drive-related tasks. Specifically, both models of the Air were faster in the file-duplication tests and compression tests.
There's much more of course, and we recommend you read the full report. In short, flash storage is a huge benefit, the battery life is improved and the current line of processors needn't make us cringe so severely.