Setting a daily word count goal will help productivity.
There are two main factors to consider when deciding on an appropriate goal.
1. Does your project have a deadline?
2. How fast are you capable of writing/typing?
Deadlines, whether external or self-imposed, are a great motivator. They provide structure for your creative goals. If you want (or need) to produce 50k words in 30 days (the basic premise of Nano) an ideal daily word count would be 2k words. This gives you a little flex room for the days when you don't meet the goal or can't write at all. The basic idea can be applied to any length work inside any deadline. (Of course, 100k words in 10 days is probably unrealistic for the majority of us.)
Your overall typing speed plays a role in determining daily word count as well. I am capable of typing 60 WPM. When I'm writing, however, my speed is usually closer to 30 WPM. (Thinking about what I'm writing, analyzing word choice, etc slows down the overall speed.) Usually I can churn out 1500 words an hour in first drafts. With later drafts (requiring more thought/analysis) it is closer to 600 words an hour.
On a normal day I have around 2-3 hours available to write. My daily word count goal is 2k.
It is important to remember that not every writer is capable or inclined to write several thousand words every day. And some churn out work with enviable speed. It is not important what everyone else does. Find what works for you and stick with it until it stops working. (Then you find something else and do it.) It is also important to recognize that, even with goals, not every day will be productive. If you only get one sentence written pat yourself on the back and keep going. If you get 5k words pat yourself on the back and keep going. The important thing is to keep at it.