According to Chris Eller :

Hello all. Just a question about 220V wiring for you. I've encountered
several 3-conductor 220V circuits recently. Doing a little research, I
see that around 1965 or so it was changed to requiring 4-conductor to
seperate the ground and neutral (vs. the old two hots and the third wire
being both the ground and the neutral).

4-conductor circuits aren't "240V circuits" per-se. They're 240V/120V
circuits. The only place where a homeowner would normally be concerned about
four-wire circuits are stoves and dryers which need both 240V and 120V. US
code now requires that new stove/dryer installations must be four wire, wheras
it used to permit 3 wire. Canadian code hasn't permitted 3 wire stoves/dryers
for several decades.

Pure 240V circuits (ie: 240W water heaters) are _still_ 3 wire. They don't
need neutrals at all.

Does anyone know if having the neutral and ground share a conductor is a
bad thing? Does having a seperate ground really help with safety? Is
some equipment effected by the N/G binding, or a seperate N and G?

Sharing the neutral and ground _can_ be quite dangerous thing, that's why
they changed the code and no longer permit it in the last remaining
exception I'm aware of in the NEC.

Ie: if you have a neutral separation in the main panel, the frame of your
stove _may_ go hot.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.