I saw that the Mateh Efrayim (or the Elef Hamagen on the bottom) brings down a Minhag to wear a Tallis while delivering a Shabbos Shuva Drasha. This is not talking about a Rov who is speaking after Kirias Hatorah, when one would be wearing a Tallis anyways. It means that if a Rov gives a Drasha at 5:00pm, he would put on a Tallis.
Does anyone know any Shul which actually does this?
all oberlander/hungarian rabbonim do this minhag whenever they give an official drasha in front of a tzibbur.
I also remember at some of the drashos given in Mir Yerushalayim the darshan was wearing a tallis but I dont remeber which drashos those were.
gedalya: it seems alot rabbonim wear one, at least ashkenazic. the two reasons are kovod to the tzibbur, and to block ayin hora, since he will be giving mussar to the tzibbur.