I do good if I only average a few hundred words per day, normally.
I decided to try and write an entire book (70,000+) during the month of July. It requires 2,258 words per day. As of this morning I am behind by just over 1,000 words, so I'm actually not doing too bad. I'm currently at 10,190. Which reminds me that I need to work on this tonight instead of watching tv.
2k+ words per day is only sustainable (for me at least) if you don't work a 50+ hour week. I'm not sure how I've been able to do it so far, other than pure force.
It's morning where I am (Japan) but I got about 2000 yesterday in two sittings. I recently decided to take on the 52 short stories in a year challenge talked about on Kindleboards, and in the last fifteen days I've got 21k words down, compared to about 5k for the rest of year to date combined. Pretty happy with that.
I killed the internet on my writing computer and probably saved my writing career.