Those who were the specialists studied more and more about less and less until ultimately they would know everything about nothing. (dotearth.blogs.nytimes.com)
The one I have heard is about knowing more and more about less and less until you get to your PhD when you know everything about nothing (nakedpastor.com)
The common joke / cliché about the Ph.D. education is that, as your education progresses, you learn more and more about less and less until (when you graduate with your Ph.D.) you know everything about nothing. (sciencemag.org)