I've been seeing this word all over the interwebs this week and it's making me a little blue. A few Novembers back, I completed a 50k NaNo manuscript. It was fun, the constant writing was a rush and all that but, in the end, the most important thing I took away from the experience was a better understanding of myself as a writer (I don't imagine that manuscript will ever see the light of day). Turns out, I can churn out mediocre prose quite rapidly and am willing to shut down the inner critic if neccessary. However, I don't particularly LIKE writing that way. And the first draft that I produced was so weak that the thought of revising it made me a little bit queasy.
I am not an outliner because I worry that if I make a list of plot "rules," my efforts to follow them may keep me from being completely true to my characters. I'm a huge fan of "and then what did s/he think/say/do...?" That said, I do a lot of character backstory work--reading the books they read, studying their hobbies. For my new manuscript, I actually went to NYC and took photographs of the apartment building in which I wanted my mc to live. NONE of this would probably count in a NaNo ms, but it's definitely writing!
I guess what I want to say is that, hey, if you participated in NaNo and wrote a 50k word ms, neat. But if you didn't get to the magical 50k finish line, you DID NOT FAIL. You were writing, thinking, learning...trying. That's what the process is all about.
So, congratulations! (And stop beating up on yourselves!)