As a reader, chapters over 10,000 words get to the point where I start eyeballing that scroll bar more and more often, unless they happen to be particularly fascinating. On the flip side, chapters under 3000 words tend to leave me feeling a bit unsatisfied, unless the author is concise and good at fitting a lot of stuff into such a small space (System:Reboot is a good example of a fic that got me to appreciate short chapters.)
As a writer, my gold standard to aim for is 7000 words; any lower or higher than that and I start to feel antsy. In practice, my chapters tend to run longer, but I'm working on being more concise. I've always had a fierce distaste for splitting chapters into multiple posts. I feel that the forum is a medium, and I should work within the limitations of the medium to the best of my ability (note: this is a totally arbitrary restriction that I hold myself, and only myself to. No one else should feel obligated to follow it!)
Interestingly, my outline for Book 2 shows that my upcoming chapters will be far shorter than the chapters I've written in the past. A side effect of being better plotted out, perhaps? (I've only slated 2-3 major events per chapter, while in the past, due to poor planning, I've had to cram 4-5 events into a single chapter and constantly feel like it's overstaying its welcome.)