Interestingly enough, I think having a Master's in English has actually made me less of a Grammar Nazi than I was before by giving me more of an understanding of how language evolves, I'm also more likely to look at "bad" grammar as simply being non-standard instead of "wrong" (one of my professors discussed how the grammar of African-American English [or "Ebonics," which, I believe, is not really the preferred nomenclature] actually makes more sense than Standard American English). If I'm editing a piece of writing for someone, I am going to point out things in it that are non-standard, but I typically don't go around acting like the "language police" (However, if people I know well are constantly saying that they "could care less," I will probably have to explain to them why that doesn't make sense).