According to Ben :
I thought I was pretty good when it comes to wiring. I thought I knew
enough to be safe and have good quality work when I do it on my own.
Then I learned about shared neutral lines for different hot phases. I
am shocked I never heard of this. No book I ever read mentioned shared
neutrals for household wiring.
Given that a shared neutral is a possibility, I don't understand how
anybody can do electrical work without shutting off power to the
entire house. You can test for hot wires and verify at least one
circuit is off, but then somebody comes along and turns on a light and
suddenly the neutral is live.

This is more of a "independent feeds into a single box" than a shared
neutral issue per-se.

In a properly wired shared neutral circuit, getting zapped by the
neutral can't happen - the neutral cannot be more than a volt or
two away from ground.

If you disconnect the neutral, then someone fires up a lamp on the
other side, yes, you can get zapped.

But:

1) Electrical code requires that neutrals on shared neutral circuits
are pigtailed, so that it's possible to disconnect devices without
breaking the neutral to downstreams.

2) There's a very strong hint that the neutral might be shared if
you see 4 conductor wire (eg: 14/3 or 12/3 plus ground). Electrical
code (at least ours) requires that, at least until the hots go off
in different directions, that it's in a common cable. Since you
can't parallel cable in normal residential wiring (eg: rejoin neutrals
after splitting cable), at least theoretically, you'll always see /3
cable where the neutral is actually shared. Past the split point,
it don't matter.

3) Because of (2), and electrical code requirements for common trip
("same strap" _requires_ common trip in the NEC, all shared
neutrals in the CEC require common breaker trip), you'll almost
always see a single cable connected to adjacent common-trip breakers
You can't deenergize one hot without de-energizing the other.

Are shared neutrals avoided where possible?

Actually, until our (CEC) kitchen counter requirements changed a few years ago,
at least two shared neutral circuits were mandatory in every house.

An electrician is about to rewire just about my entire house. Should I
request no shared neutrals or is this a silly request?

I wouldn't worry about it. Most of the concerns about neutral stupidities
regarding what you've read is for industrial wiring botches, which is largely
inapplicable to housing.

The electrician probably won't be tempted to use it much anyway.

What you _should_ do is insist that the electrician use tie-barred/common
trip breakers everywhere he'd consider using common neutral (or two feeds
into the same box - even a switch box), regardless of whether the NEC requires
it for that specific instance.

The only times I've ever been zapped is where the electrician violated
the CEC rule about having non-common-trip feeds into the same box. They
weren't shared neutrals.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.