Ever since starting graduate school I've tried to make scientific reading a part of my daily ritual; I track pages read using Beeminder, and the graph doesn't lie. It keeps me honest.
I aim to closely read and summarize 5 pages per day and skim a few other abstracts besides that. I spend about half my time looking at data and figures which doesn't contribute to my daily "page count." When I'm reading about a new topic these five pages can take several hours, but on topics I have more background in five pages might only take an hour per day.
I guess since everybody defines "read" in a different way it's hard to get an objective answer about how much reading is enough. How much people read seems like a bit of a sensitive topic among real-life colleagues because everyone has a bit of anxiety that they aren't reading enough. But for those further along in their academic path, I'd like to hear how you approached the literature early in your graduate school career and what you think is a sufficient amount.
I guess this all distills down into two main topics:
When deciding what to read each day, should I focus on depth or breadth?
Is five pages of close reading per day enough? I know it doesn't sound like much, but it takes significant mental energy to meet that goal. And consistently reading 5 pages per day adds up to a lot over time.
Edited to add: I mostly read about petrology, volcanology, structural geology, and tectonics if that makes a difference. By "page" I mean "page of text" so if I'm reading a structural geology paper with lots of maps and figures I discount for those and a "ten page" paper becomes a 5 page paper for my purposes.