When does one respond “Baruch Hu Uvaruch Shemo”?

The Shulhan Aruch (O.H. 124:5), citing the Tur, says that one responds “Baruch Hu Uvaruch Shemo” (lit. “blessed is He and blessed is His Name”) to any blessing that one hears and at any time. The Shulhan Aruch makes no distinction between a blessing through which one is having one’s obligation of a particular Mitzvah fulfilled, such as one listening to Kiddush, and any other type of blessing. 
The Mishna Berura (M.B., O.H. 124:21), on the other hand, cites sources that say that one should only respond “Baruch Hu Uvaruch Shemo” to blessings that are not being recited on one’s behalf, such as if one’s fellow is reciting Birkot Hatorah during an Aliyah, and the like. For blessings that are being recited on one’s behalf, such as those for Kiddush, Shofar or Megila for example, then reciting “Baruch Hu Uvaruch Shemo” can be considered as an interruption. In other words, just as one would not interrupt one’s own blessing, the same is true when one is listening to a blessing said on one’s behalf, according to this approach. 
The HIDA (Birke Yosef, § 124) says that although there is a stringent approach not to respond to blessings said on one’s behalf, the custom to do so should not be challenged. 
Rabbi Baruch Toledano (Kitzur Shulhan Aruch, pg. 101) says that the custom to respond “Baruch Hu Uvaruch Shemo” should be upheld, especially in light of the fact that he considers it part and parcel of the blessing itself. Indeed, when people are overly stringent, then they may forget to recite “Baruch Hu Uvaruch Shemo” even when a blessing is not said on their behalf, in which case all agree that is must be said. Thus, when people are overly cautious about reciting it, the significance of “Baruch Hu Uvaruch Shemo”, which is an important praise of Hashem, is greatly diminished. 
Summary: Baruch Hu Uvaruch Shemo is recited when one hears any blessing.