I'm not being obnoxious and my monitors are usually dimmed because it's easier on the eyes. But I really have to strain them to read some of the more pretentiously designed sites.
I wonder why books are printed with black ink. Is it because publishers have bad designers? Or because the text is more legible that way?
There's actually a difference there, though: books aren't a light source. When you're reading a book, you're reading it with indirect/reflected lighting. This really does make a difference with respect to eye fatigue. And, for that matter, think about the difference between reading in your living room with nice ambient lighting and trying to read the same book in bright sunshine in midday. The "white level" is much higher in sunshine but the black level remains about the same -- in other words, there's much higher contrast -- and it's harder to read.
It's certainly possible to go overboard with low contrast on web pages, but most of the research I've read suggests that there's a happy medium. What you want to aim for, IIRC, is around a 50-70 point difference in lightness on the LAB color scale between the main background and main body text, at least if you expect to be throwing article-length text at people rather than Twitter-length text.
Black ink is far from black. Your monitor's black is also far from pitch black, but the whites are much brighter than paper (emitted vs reflected light), leading to huge contrast.
What designers are trying to achieve by setting text to #333 and background to #f9f9f9 is exactly making screen contrast more like a book.
By lowering your screen brightness/contrast an unusual amount, you're solving the problem for all sites doing it wrong, but turning the ones who use proper contrast into crap. Who's to blame?
I wonder why books are printed with black ink. Is it because publishers have bad designers? Or because the text is more legible that way?