I'm back again this year too. This is my fourth year. The first year, I only wrote for one night, tehn didn;t pick it up again. year two, I wrote slightly under 80k during the month, a novel I am now trying to find an agent for. Last year, I wrote to 50k and stopped, because I knew that despite havinga good story, the novel needed major reworking (change in POV) and writing further wouldn';t do me any good.
This year has been a bit different for me. In years 2 and 3, I crossed the 50k line by day 10. This year has been a lot slower. I find myself writing once every two or three days. So far, the story is still working, it just feels different. I'm sure I'll hit the 50k, and my aim is somewhere between 75 - 80k for the month.
To answer questions above (even though they are a few days old), I think people approach nano for different reasons. Some want to write 50k words, just for the challenge of writing a 50k word story (or sometimes just any 50k words)--they are looking soley for the challenge. Others have a story in their head they'd someday like to write--what better way than nano? Some take nano seriously and write a book that they intend to attempt to polish and publish someday. Make no mistake, anything done in NaNo will be a rough draft, but that doesn;t mean it doesn;t have potential after a bit of sweat and polish.