For what it is - and putting cost aside - it's a perfectly capable machine. I have a first generation 1.8 model, and while I wouldn't use the PhotoMerge function in Photoshop it's perfectly capable of maintaining a modest Lightroom catalog on the road. Specifically, injecting images, key-wording and a spot of image adjustment. In my case I'm a relatively low volume - call me old fashioned - non professional. As a general productivity machine it' great alongside something bigger back at base.
Depending on your intended volumes and trip length you may find the small, slow (4200rpm) and difficult to upgrade internal hard drive a problem. I use a D3 - with dual CF cards - I don't recycle CF cards so the MBA is effectively the third location of the RAWs. You might need to consider external USB drives. Unfortunately this starts to defeat the idea of the MBA's small size/weight in my view.
The other option is a Unibody 13" MB. They can be fitted with more RAM and much larger, faster (7200 rpm) HDD. It's just a damn shame Apple didn't add a FW 800 for external drives.