Yes, I did have an NSF (and during my dissertation writing year, a different external fellowship), which helped tremendously. I had no teaching or research obligations so I could focus solely on the diss. And fair point - working on my dissertation this way meant that I finished it in 9 months (exclusive of data collection), which is fairly quick. But a person could work fewer hours on it and just take longer - not necessarily a whole lot longer, but I think 2-3 years is more normal. I just really, really wanted to get done.