I notice in Minyanim that I participate in that when the Chazan repeats the Shemonei Esrei and gets to "Baruch Ata Hashem", nearly everyone says "Baruch Hu UVoruch Shemo".
Yet, those same people skip other places where Hashem's name is said. Why, for example, doesn't "Refaeinu Hashem" get a "Baruch Hu..."?
Moreover, why don't people say it when hearing someone is saying Birkos Hanehenin/Tachanun/Shir Shel Yom (all places where one can interrupt)?