As I use calibre's viewer, there's one thing that repeatedly surprises me -- the boundary / end of the current "page" (source page, not what the reader tries to present) is not obvious to me. Consequently, when a boundary is crossed, the transition is sudden and often unexpected. To cope with this, I've temporarily enabled the following in Preferences -> General -> Page Flip Options -> Line scrolling stops at page brealks. This prevents the sudden transition, but I'm wondering if there is some way to get visual feedback about page boundaries instead with the ability to scroll across boundaries...
Any ideas?