When I was at university, my English teacher used to insist a lot on the difference between these two expressions, telling us that even if was to be used when introducing a hypothetical situation (Even if I knew where John is, I wouldn't tell you), whereas even though was to be used as a concession or admission (Even though I know where John is, I won't tell you).
A few years have passed since my university days, and I'm under the impression that this kind of distinction is no longer made. Even if seems to be prevailing, and even though is less frequently found either in texts or in speech. Is my feeling correct? Has the difference between the two forms been cancelled?