To me, PEX is something used in trailer homes.

Actually, the grey polybutelene (PB) pipe was most commonly used in
trailer homes. It didn't have a long track record, and did develop
problems after a few years. (Got brittle and crumbled after a while I
think). In our old mobile home, the problems were caused by staples shot
into the water lines by the builders...

PEX is a cross-linked polyethelene that has been around for more than 30
years for radiant heating and potable water supplies. It has a long track
record of reliability.

Real houses use rigid pipe.
Either copper (preferred) or galv. steel.

First, copper is getting rather expensive these days (pipe, wire, etc.).
More importantly, copper is prone to damage from freezing, and develops
pinhole leaks when exposed to acidic water. It also requires a torch to
sweat the connections, which is a very real fire risk.

As for galvanized, it rusts and corrodes badly. Leaks are common, and it
slowly fills up with rust till the water supply is completely cut off. I
just replaced the entire plumbing system at my in-laws house because the
pipes had rusted to the point they didn't have water anymore. Galvanized
is also slow and difficult to install.

these days everything is some sort of plastic and nothing seems to
last more than a few years anymore.

Plastic lasts a very long time (100+ years supposedly). The problem is
when it's used in "stress" situations. In other words, tools and other
items that rely on strength shouldn't be made of plastic.

we are all paying high prices for gasoline these days

Go take a look at copper prices...

the manifold approach is used and supposedly makes for
better water pressure.

I don't know if it helps with water pressure, but the main reason for the
manifold system is to reduce the number of fittings in the system (the
most likely failure point).

how many homes have numerous plumbing fixtures all being used at once?

Dishwasher is washing dishes, refrigerator is filling the ice tray, I
just flushed the toilet, and am washing my hands. It's not difficult to
use multiple fixtures, even if you live alone.

If I had to replace my own plumbing right now, I'd use copper.

I researched the many plumbing options when we plumbed our house.

Copper was the obvious choice, but our acidic water would quickly cause
problems with copper pipe. Sweating the joints is also a fairly slow and
laborious process, and I wasn't crazy about wielding a torch in our brand
new house. Too easy to start a fire. In addition, copper was already
getting expensive by that time.

I was very interested in PEX, but at the time it was difficult to find
locally and the tool required for the fittings was expensive. I opted not
to use PEX because the supplies were not readily available, which meant
long delays if I needed something I didn't have. I also didn't want to
have problems in the future if I needed to make repairs or alterations.

In the end, I went with CPVC plumbing. It's inexpensive, widely
available, quick and easy to install, doesn't require any special tools,
is lightweight, and impervious to acidic water. However, knowing that
plastic often breaks under stress, I used brass drop ear elbows at each
fixture.

plastics are never as good as metals.

Different materials for different purposes.

Plastic excels in situations where you need light weight and resistance
to corrosion.

Metal is better for items that need strength to endure physical stresses.

I wouldn't want a plastic rake anymore than I want steel garbage bags.

Anthony