Saying G-d's Name unnecessarily, is a very serious matter. If someone recites a Berakha (blessing), with G-d's Name, when it is not required, it is considered to be taking G-d's Name in vain. Those who hear someone recite a blessing unnecessarily, may not answer Amen after it.
If someone mentions G-d's Name in Hebrew, without knowing that it is forbidden to do so, the one who hears it should caution him about this and let him know that it is forbidden and that he should not do it again. Even one who mentions G-d's Name unnecessarily in a language other than Hebrew, should be told not to do so.
If someone wishes to say that G-d did such and such for him, one must not interrupt him after he says G-d's Name, but should let him finish his sentence. To interrupt him will cause him to have said G-d's Name in vain. On the other hand, if one hears someone mention G-d's Name in order to curse another person, then one must make a point of interrupting him to prevent him from sinning by cursing with G-d's Name.
See Shulhan 'Arukh, 215:4. Kaf Hahayyim, ibid., Oth 22, 25, 26)
Taking G-d's Name in vain, not answering amen to a bracha levatala, berkha lebatalah