So, I'm halfway through, as are most of the other guys...
My feedback from this point is:
I'm not sure I like this format. I know the point of NaNoWrMo is that you should just get it down, and worry about quality later, but it does tend to mean that readers are getting a first draft that looks like a final draft. It seems to be that one idea a day is compulsorary, and if you don't have a good one, well, Heaven help you.
It wrecks your web life. I mean, I'd like to be over on Matt's blog commenting on his faeries, but I don't have the time to enjoy his stuff now because I'm busy with mine. That does sort of suck. It means I haven't podcast a book chapter in months, I haven't researched any proper, paid writing for a couple of weeks...it kind of steals a lot of time you'd like to spend on other endeavours.
On the positive side, I think it forces you to write in a way that leaves you loopholes for future ideas, which is interesting. There's this tension in Ars books: sometimes as an author, you lay down a beat, and you hope someone will pick it up eventually, or you yourself pick it up a few years later and say "See, I played for that. I passed the ball to myself, there. Tricky, eh?" but on the other side, there's the attitude that if you have good material, you should just go with it, because who knows when the book that better suits your ideas, on say, theatrical masks as magic items, will come up? You might as well just use your best gag, because you don't know when you'll next be at the microphone. This format lets you play that game in minature, and its a very interesting way of writing.
It also forces you to make do. I've been watching a show called Mastercrafts, which is about people learning to carve stone, or blacksmith, or make stained glass windows. The thing I keep taking away from it is that its the artsy ones who generally fail to produce useful work at the end. Writing's like that: there's an element of actually needing to hit the deadline, even if the work has less research in it that you'd like. Fortunately I have a sort of reflex so that I come to loathe reading my books, so I stop fiddling with them. The thing about NaNoWrMo is that it hits you with a deadline each day. Now, this forces you to publish stuff, even if its bad, which is bad, but at the same time, it does get you into the mindset that the book is a product, and it has a deadline, and its not about making the perfect book, its about working the various resources you have so that when the deadline hits, you have somethign which is about as good as you can hope. The mindset is interesting, even though it means you, the reader, are getting the sort of first drafts I leave for a few weeks before reading again, then rewriting, then circulating for comment, then rewriting, and then sending out to playtest. I can see that for new writers, particularly, this "perfect is the enemy of good" situation is useful training.
If I did it again, I'd cheat harder. I'd research more before the kick off, and have more pieces prewritten*. Earlier I was a couple of days ahead, and because I laid down some beats I'm going to be able to take it easy in the last week, since those objects have some sort of idea behind them, but the halfway point is a sort of annoyingly humpish bit I need to get over.
Also, of course, only a handful of people are reading them. I'm going to finish them, but at the same time, I could have been podcasting for my Year of Reading project, or reading up on some other folklorish thing, or writing my new game about failed colonisation attempts, so there's a bit of a tension there as to how self-indulgent I should be with my writing time.
*I wrote a couple on Halloween...but given I've said I'm not following the strict rules, I don't much care. 8)
The saint a day aspect has run in to several problems -- I feel vaguely impious in presenting game mechanics for the saints cultus, and am uneasy I may offend good pious folks, or pagan folks, or radical atheist folks, or just folks really. I'm even more concerned i may offend the saints. Religion is a touchy subject. I'm trying to treat the saints with respect, which is actually rather easy as they generally have many admirable qualities.