We would be seeing far more cases, even here in the US, if Ebola were a true airborne disease (since Dr Kent Brantly first set foot back in the US). However, it is true that Ebola is very contagious in the sense that it only takes 1-10 virus particles to infect someone (under "infectious dose" section).

As the WSJ reports, this Spanish nurse followed all the infection control protocols and only had contact with the patient twice--once while he was alive and once after he was deceased. Like I said earlier, a lot of people in healthcare are going to be grappling with the implications of this incident.

Speaking of airborne transmission, here is a good explanation in Scientific American about what is involved when people talk about Ebola mutating to become a true airborne disease and how there is little evolutionary pressure for it to do so. The risk of such a drastic mutation appears very low because the fundamental nature of Ebola and how it attacks the body would need to change to accommodate such a change.