I'm going to go redirect you all to this post by John Scalzi on his Whatever blog. Because I didn't know professional writers didn't like NaNoWriMo. And Scalzi makes some awesome points for it. Which means my respect for him just increased a smidgen.
I'm not participating in NaNoWriMo, but I know people who do and I admire them. Because it's hard being a student and writing 2,000 a day. Seriously, it is! There are papers to write and odd-ball things to read for classes. And THEN you have to do your personal work. And if the personal work doesn't get done, your weekends are suddenly so much more cramped with things to do than usual.
Keep working NaNo writers! Don't give up just because it's close to slum week! Add a new character into the mix. Continue the story. Write random scenes from random places in the plot! Just keep going because those 50,000 words don't have to be the most gorgeous writing you do on the planet. Just get it all done!
Also, when you're finished, print off your entire story and drop it. That's right. Drop it on a nice, hard floor (not carpet) or a table for the satisfying whump of completion. My friend DanPan said it does wonders.