MacWorld’s First MacBook Air Lab Tests
2008 January 26
Our tests reveal that the slower processor and disk make the MacBook Air quite a bit slower than the other portables in Appleās product line. The MacBook Air was also outpaced in our tests by the its closest desktop cousin, the ultra-compact 1.83GHz Mac mini Core 2 Duo.

Not surprising when you talk about a machine that puts size/weight first. Nonetheless, the MBA’s performance is yet another indicator that it is a niche product and almost certainly not a primary machine.
It beats a 1.67 GHz G4 in most things. That’s something, right?
http://theocacao.com/document.page/545
There’s some intelligent discussion of this topic.
Of course it’s a niche machine. All machines are niche machines. The important question about Air is, does it provide something valuable to a large set of people who haven’t previously been catered for to the same degree. Clearly, yes.
The number of people who unthinkingly answer “no” to that question solely by virtue of not being amongst that set has been, politely, surprising, lately.