I did "win" NaNoWriMo for 2014 - finishing with just over 50,000 words in 30 days. It's not actually that much in terms of output - typing at 30 words per minute (i.e. how fast I can type if I'm thinking rather than copy typing) your daily ration of 1,670 words should take less than an hour. In practice, it never took less than two hours because "thinking", having yet another cup of coffee or crossing out a paragraph and writing it again with different characters or the same characters in a different mood always tended to happen on a regular basis.
The majority of the writing was simple enough. I took the first two days to write a 2,000 word synopsis that expanded to a 3,000 word synopsis by the end of the month, and did one major reorganization in the middle when I realized that the division into 9 sections (flashbacks alternating with the present day) had shorter sections at the beginning than at the end, a sort of reverse speeding-up-like-Stairway-To-Heaven that would drag everything down at the end. (Or, of course immerse every reader more fully towards the end and make them think the whole experience had been that deep - but you can't second guess everything.) Making it into 11 sections solved that problem, meant that I could add 1976 (one of my favorite years) to the mix and delay the denouement for a little while which may (or may not, but see above) create a bit of tension about how it is all going to turn out.
Fifty thousand words actually only comes to section 8, so three are still to be written. A fair amount of the beginning sections are of the type, "and then he got really lucky and so this happened and then that happened", which obviously need to be expanded - so there's probably thirty thousand words yet to go. Then of course, comes the editing and polishing, which can take between one read-through and the rest of your life, depending on what sort of writer you are.
One part of a middle section is completely unwritten, with just a placeholder under the chapter heading, because I honestly don't know what happened to that character at that time. Hopefully it will become clearer before I have to write the rest.
One great thing about taking a run at it, as you're forced to do given the time limit, is that you can probably remember what you were thinking and why you were thinking for the majority of the writing. I had a synopsis, but they aren't much use for details - obviously if they were detailed, they'd take as long to write as the actual text. For example, if you last saw your main characters in a bar, wrote a different scene and then went back to the bar, you have to remember some important details - what the bar was called, the time of day, who was there, how many drinks they'd had, what mood they were in, whether you'd mentioned the brass kettles on the walls already or not. A couple of times I had that continuity problem you occasionally see in movies where one character's drink moves from one hand to another between shots, and also the type you get in books alone, where somebody becomes dismarried all of a sudden or his wife's name changes from Rita to Consuela and back over the course of a few chapters.
There are special word processors designed to get over this type of issue. I own one, and can't remember what it's called because I don't use it very often. As with making a synopsis that is complete, filling up a database of characters, names, ages, likes, dislikes, times of day, amount of action in the scene, amount of emotion in the scene, whether the emotion is getting higher or ebbing away in that scene and so on takes longer than writing the book, though it's perfectly possible that if you do it correctly, the software then just writes the book for you. I've never got it to that stage to find out if it does.
Ah! It's called Power Structure - I went to look at its box. It's very very powerful but as I say, filling it up seems to be the hard part. A number of writers, including professional writers, swear by Scrivener, which doesn't cost a lot and seems to do most of the things Power Structure does. Once again, though, is the learning curve harder than actually writing the novel? (I'm sure the first person to not bother to learn Excel is very happy with his calculator to this day, and has only lost a few hundred hours by not putting in the time to learn the program.)