This revelation so ingrained in pop culture at this point that the case above is very rare. I've talked to people who literally knew nothing about Star Wars (and I do mean nothing), never watched the movies, but they were familiar with "I am your father" from ESB.

What's worse, though, is the fact so many people got spoiled by the atrocity that is PT, which they hated anyway. That just makes me sad. And glad that I got to watch these when there was no PT and/or widely available Internet access to spoil everything for me.