I don’t believe that the overall page length itself is inherently problematic. I have noticed though that in many responsive designs, purposeful groupings of content are easy to spot on larger screens, but get muddled when things start to stack on mobile screens.
This is probably mostly a problem on “content” sites in which you smash things down into the ol’ tube of content. I don’t mind the tube, but I think Kevin is doing some smart thinking here. There are plenty of different patterns that can happen while tubizing, and it’s probably not thought about enough.
This site is particularly guilty. A quick document.documentElement.offsetHeight test showed 14749px, more than double the height of an example Kevin pointed out that was a bit excessive.