Mainly, it makes scrollbars completely impossible to use for actual scrolling. Try using one of these sites loading more and more content without scroll wheel or something similar.

I'm going to have to agree. Another problem with endless pagination is that it makes it difficult for me to refer to content.

For example: "Look at the blue shirt on page 5" rather than "Look at the blue shirt visible after about 30 seconds of scrolling down"

Also, when the page is reloaded, I have to scroll all the way down to where I was (which may take longer than I want it to because the page needs to load everything before my target).

Sometimes I think I'm the only person who doesn't see scroll bars anymore. Does your mouse not have a scroll wheel? Does your trackpad not have 2-finger scroll?