Infinite scroll is usually terrible with browser navigation. If you can assume that the user stays within your page and doesn't need to navigate back and forth, it may be a reasonable option.

But for something like Tumblr or Pinterest, it's awful. When the user sees an interesting post, she clicks on it to open the page. Then she navigates back to the main page. But wait -- the infinite scroll's contents have been lost on reload. Now the page shows the top of the scroll, rather than the position where the user actually was when she clicked a link. It may be a long, long way to scroll back to where she was, with numerous loading progress indicators along the way...