I hate it as a user, it needs to die because it makes my user experience so much worse. I've never seen a not-broken implementation. Suddenly, the end key cannot take me to the bottom of the page, using the browsers native search function (which I will always chose over an in-page alternative) cannot do its thing, I can no longer get an idea of how far along I am in the list, and I cannot do a quick visual scan of many items because dragging the scrollbar does not behave naturally. Page up and page down is all but broken.

A compromise may be a browser option that one can set globally to indicate whether one wants pagination (and how many results per page) or infini-scroll.