How much do you write each day?

"But how much should you really be writing?" people in creative writing classes ask, looking for the set number, the goal to work towards, something that has been approved by Someone Else.

"It depends," is what you say, because it's all you can say. It depends on so many things.

Are you writing a first draft, or are you revising? (Writing 1000 words is not the same as revising them.)
Are you revising as you go, or just powering through?
Do you know exactly where the book/story is going, or do you need to factor in thinking time? Or research time?
How much time do you have per day? Per week? Per month?
How much can you reasonably write within that time?
What's your limit for 'workable' words per day/week? (e.g. you can write 1000 words a day and know they'll be okay, but going to 2000 words will mean that there's unusable rubbish in there)
Can you write at the same pace throughout the week? When will you take breaks? (Taking breaks = good thing.)
Are you under contract for this book? When is it due and how much do you need to write per day/week/month to meet that deadline?

Would love to hear your answers on this one, everyone! How much do you write each day that you write – and is that every day, every weekday, every second day, or occasional days only?