This is an issue I've been thinking about some, especially in the context of stories on the web. How long of a webpage is too long? When you see a wall of text, do your eyes glaze over? Do you hit the back button and find something else to read? What if you want to post a long article or story on the web? How do you go about doing it?
One issue is that long webpages are intimidating. You watch the little scrollbar shrink to invisibility, and think that maybe it's not worth it. Then again, if you decide you do want to read a long story, can you do it in one sitting? Probably not. But if you go away and come back, how do you find your place again?
One option is to split it up into a number of pages. More than one blogpost, or an article that spans multiple pages. This may work, but a lot depends on the software you're using, and how easily you can do it. Once you have multiple pages, you need to put some effort into making it easy to get from page to page. How many pages are there? If there are three, it should be relatively easy to find your way and come back to where you left off. If there are 20 or so, you might become lost, and forget where you left off.
If instead you keep it all on one long page, you run into the issue of losing your place, especially if you navigate away and then come back. You can simplify that with headings, but it's still a pain to scroll down to the correct heading, and you may miss it and scroll right past. Fortunately, webpages can include anchors, which allow you to hyperlink to certain parts of a webpage, including from in the same page, such as I did in my Brief History page. Unfortunately, the blogging software doesn't always handle anchors that well. It took some effort to get that page working right (including modifying the html and not switching to the WYSIWYG view, which allows Blogger to mess it up).
In either case, navigation is key. If you're using multiple pages, then you need to link to both the previous and the next page at both the top and the bottom of the page (you need to be able to go back from the top and forward from the bottom, but it also helps to be able to go forward or backward a page at a time to find your place without needing to scroll to the top or bottom each time). You should also have links either to all of the pages, or to a table of contents. If you're using one long page, you need to have periodic links to the table of contents on the same page. This could alternatively be done with a separate frame that displays the table of contents at all times, but that requires you to muck around with the html of the page. Blogging software generally can't handle that for you.
So, you see, there are a lot of issues involved in getting really long posts to work. I'd be happy to take suggestions for any other tricks.