I love National Novel Writing Month. I believe it teaches important lessons for beginning writers—and provides a reminder for more experienced writers. Putting pen to paper (literally or figuratively) is the most important things. Tough days come and go, but keeping up your writing momentum is crucial.
"Inspiration usually comes during work, rather than before it."
That said, fifty thousand words in one month is not always feasible, or productive. I would love to participate in NaNoWriMo this year, but I simply don't have the time or energy. I know it would lead to burnout and have a negative impact on my work.