I've come across a number of PhD dissertations recently that are something like 3 chapters/100-135 pages long. I've also heard that more and more programs aren't even requiring dissertations anymore for the PhD, but only several (e.g. 3-4) standalone articles. Both trends -- if they really are trends -- seem problematic to me.
Although I have some vague worries about fairness -- how is it fair for a discipline to award some people PhD's for 100-page dissertations but others PhD's for 300-pagers? -- this isn't my real worry. My worry is that the practice discourages ambition and systematic thought. Most of the great philosophers -- Plato, Aristotle, Kant, Heidegger -- didn't just hammer away at small problems; they developed entire systems of thought. And the same is true of more recent people of influence: Quine, Rawls, Davidson, etc.
I don't mean to suggest that we should all aspire to create grand philosophical systems. All I mean to suggest is that it is important for philosophy to encourage systematic thought, and to do it early on. After all, as David McNaughton points out, if you don't learn to do it early on -- if you develop deep habits of attending to narrow problems -- it seems unlikely that, all of a sudden, you'll learn to do later on in your career. Habits are not easily broken.
What say you, fellow pupae?