I took part in 2013 and completed the goal of writing 50,000 words in 30 days. Here’s part of what I said about the experience at the time:
We take writing for granted because it's an everyday task, something the average person with a high school education can do, but to put together a story good enough to be sold on the market? I don't care whether you're the hackiest hack writer that ever owned a typewriter or Stephen King, it ain't as easy as it looks, and I have new respect for anyone who does it on a regular basis.
People on the NaNo message boards planned trilogies and even entire series based on what they created. Perhaps it comes as no surprise that many of the participants I saw worked in sci-fi or fantasy, unlike me. I thought they were crazy, that they should concentrate on finishing one book first.
At real-life NaNo writing sessions, I didn’t make many new friends. I cared more about writing. 50,000 words seemed daunting. Completing it as soon as possible was my concern.
It was tough.