I'm on another machine right at the moment but I believe I've got about 42 GB available on my SSD MBA. I did the "clean install" and got rid of stuff I didn't need (printer drivers, Garage Band, languages, etc.) and have installed very little on the machine so far. I haven't put my iTunes library on it because I can access my music with my iPhone if on a trip. I don't use iPhoto and I haven't installed Aperture on that machine. I did install Photo Mechanic, though, for reviewing images after I've uploaded them (temporarily) to the MBA while on a trip. My main use of the MBA around home has been for email and web surfing, and will be the same while traveling. I'll also be uploading from my digital camera memory cards to the MBA when on trips, but will save the heavy-duty image post-processing for when I return home to the Mac Pro.
I love the MBA -- it's terrific for everyday web surfing and checking my email whether at home or away from home.