I was just in the store to see it live and I won't be original, I'll repeat what has already been said here:
- the photos don't show how it looks at all,
- it's a chameleon color, depending on the angle and light it looks completely different,
- from the perspective of the user's eyes it looks dirty silver / very light gray, the blue is mainly visible on the outside casing at a fairly large angle,
- in the store the light source was exactly above the MBA, (Howard2k don't read this) Sky Blue also reflects light quite a bit, although it seems a slightly less reflective than the silver one,
- in the store it was next to Midnight Blue and these two colors couldn't be more different. Completely two ends of the spectrum,
- in general I agree with the previous speakers, it looks very classy, one of the most premium Apple colors, if not THE most premium one.
Edit: Just to add a little note for those who are torn between Sky Blue and Midnight Blue. If you want the rest of the world to "disappear" and have only the screen in front of your eyes to get into the "flow" now that the Space Grey is gone then the only option for this is Midnight Blue. I realized this when I saw them next to each other.