Has anyone tried using a Macbook Air?

Yes, this is what I use with Audirvana Plus. Could not be happier with the set-up, see my previous post on this subject.

http://forum.audiogon.com/cgi-bin/fr.pl?ddgtl&1364947210&openmine&zzMgattmch&4&5#Mgattmch

I use my Mac Mini without a monitor, keyboard or mouse; no clutter at all.
I owned a Macbook Air a coupel years ago and used it mainly for interweb surfing. I believe they have changed them, but mine was the most uncomfortable to hold laptop I have used. The edges of that machine were so sharp it wore the skin off my wrist.

I currently use a 2010 MacBook Air as a server with a Western Digital external drive. It replaced a very old Mac Mini, it was a early intel version. The ram was max out at 2 gig's. The Air was my personal computer. The screen is only 11 inches and had become too small for daily use. I upgraded to a larger screen computer, gave the still perfect Mac Mini to my sister and transferred music server duties to the Air. Also the Air has only 2 gigs of ram.

With regard to iTunes music playback, no real listening change. Yet, Screen Sharing and all remote functions improved. Every click is quicker.

Good Luck

Some Mac laptops have a pretty sharp edge. Sandpaper fixes this right up.

I used to use a standard config MBA (13" 4GB RAM 128GB SSD) 2011 for normal notebook duties that did double duty for audio when I am on the road and it is passable. But I found my 2010 Mini which was dedicated for music (no extra apps) sounded better.

If you use a Mini, you can enable Screen Sharing after you have set up the system to allow you to remote control the Mini from an iPad or another Mac (or even a PC with a VNC application). So you wouldn't need a keyboard or monitor in your hifi rack.

If you want to use a MBAir for music, I'd recommend the following:
make sure you get the 2011 model or newer. The older model did not support Thunderbolt so your only interface is USB2.0. Ideally you want one interface for HDD (storing music) and another interface to the computer audio. With TB, you can use TB for an external hard disk or a TB-Firewire interface for external hard disk. Your USB is then dedicated for connection to the DAC.

Also try to load it up with as much RAM as you can fit (the RAM on the MBA is not upgradeable). 4GB is the bare minimum. 8GB is the max you can fit and there's never too much memory. My new Mini is fitted with 16GB :)

I found 128GB SSD is sufficient if I use it only as a dedicated music server.