Over at Academic Inspirations, Dr. O brings up a great point about dissertation writing:
On the contrary, grad students should be continually writing throughout their thesis work, one results section at a time. For papers, if possible. If not, then for practice. Writing is an art, and it takes lots of practice. You understand your data and results better when you have time to write and reflect on them. Speaking on those results is important too, but unless you can convey your message on paper, you're doomed.
So grad students, start writing now.
Yes, yes, and more yes. For some of my students, I've had to structure them a bit, coaxing them to get me a draft of a manuscript--even if the results aren't all in yet--but such-and-such a date, just so that they get in the habit of writing about things while they're fresh in their minds and they don't procrastinate and put off starting the manuscript for another month (or 6). Grad students, it's a great habit to get into RIGHT NOW--write a bit every day (or every week, if you're like me and prefer to vomit papers up in larger chunks)--just get into the habit of doing it regularly and you'll be way ahead of the game when it comes to your thesis or dissertation.