One of my proudest moments was when I finished a 300+ page novel up to and including a finished second draft. At the time I was pretty pleased with myself, at least until I realized I'd worked on it to the point where I never wanted to see it again. Short attention span > pride.
Other than that, I guess when I backpacked around a couple foreign countries, which might not sound like something to be especially proud of until you realize that unless I'm going to work it's hard to motivate me to get out of bed.
I can definitely relate
The biggest novel I've read was Stephen King's The Stand (which was over 1000 pages). Pretty addicting book, might I add. And well made