I don't understand how people do this unless they just read really slowly. It's maddening to try to do and have it actually be where you're reading. It also kills me that HN seems to embrace this practice, yet is also so incredibly skeptical of SSS and dyslexia.
Unless you write one-sentence paragraphs, this turns out not to slow things down at all. (I read at a "normal" pace and sometimes do this.)