Giluy Milta B’alma has a post about the well-known piyyut, Yedid Nefesh (ignore the version of the piyyut included in this entry, see below), that is recited on Friday night in many synagogues. The post describes the textual history of the piyyut and why it is attributed to R. Elazar Azkari (1533-1600). Pay attention to the comments about variant readings and you’ll see why most siddurim and birkonim probably have an inaccurate version of Yedid Nefesh. See here for a more correct one. I know that Siddur Sim Shalom has the more accurate version, based on a manuscript at JTS, and would appreciate anybody pointing out others which also do (Koren-Sacks might be a good guess).