On the basis of what I've heard people (in the Midwest of the U.S.) say, I have the impression that: (1) Mathematicians say "formulas" but philosophers say "formulae". (2) Buildings and television sets used to have antennas atop them (before cable became common), but insects and little green Martians have antennae. (3) It is indeed dangerous to form "classical" plurals carelessly; I've heard a university professor use "quora" as the plural of "quorum".

On the basis of what I've heard people (in the Midwest of the U.S.) say, I have the impression that:

1. Mathematicians say "formulas" but philosophers say "formulae".
2. Buildings and television sets used to have antennas atop them (before cable became common), but insects and little green Martians have antennae.
3. It is indeed dangerous to form "classical" plurals carelessly; I've heard a university professor use "quora" as the plural of "quorum".