i tend to only read on trains and buses, to and from work, so i generally only get in about an hour, hour and a half of reading a day. Though my girlfriend and I split up recently so i've been reading much more at home the last couple of months. It took me three months to read Infinite Jest. It took me a whole year to read Gravity's Rainbow, but I was reading it for a couple of months, putting it down and reading something else, then picking it up again. I started Robeto Bolano '2666' a couple of weeks ago, i'm about 300 pages in, so i'm getting through it quicker than I expected, but the language is so beautifully simple so that's probably why. I'm only reading pretty long books at the moment so i'm definitely not one of these two-or-three books per month people. And I really only ever read fiction these days. This forum always makes me feel like i should go back and re-read all the Deleuze and academic theory stuff I read at university, because i've totally forgotten it all, but I can't bring myself to do it, because I just enjoy reading fiction too much.
I'm totally with luka, benny, empty mirror etc on forgetting pretty much everything about a book after i've read it. It's infuriating.
I pretty much always stick a book out until the end, even if i'm not enjoying it... unless it's really terrible.