This may be a dumb question but could it be possible to have both?  With
the mirror lockup available on many DSLRs could it be used to allow the
sensor to get a continuous light feed and then send the image to the
LCD?  You just wouldn't have both, the view finder and the preview at
the same time.  I remember reading somewhere that CMOS type sensors get
hot when run continuously so maybe that is a problem.  I'm sure I am
missing something or it would have been done by now.

It's true that doing it "the way  most point & shoot users seem to do"
doesn't work very well.

However, you can actually hold the camera much *more* stably out in
front of you than you can up to your face.  Trouble is, with a DSLR
(or film SLR) you can't see through the viewfinder then.  With a P&S
you can, and for a P&S it's a better approach when stability is at
issue.  

Detail explanation in a previous message this week.  If you're using a
P&S hand-held in low light, you really need to try this.  If you've
got a digital camera it's easy to check -- take a dozen pictures each
way at each of a series of gradually decreasing shutter speeds, and
see which way gets you sharper pictures.  (Of course practice with
either technique will improve your results!)  (Okay, you can perform
the same test on film, it's just slower and more expensive.)

Very difficult with an optical VF, less so with an EVF.
There is this though:

<http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=3
7321&is=USA>

Nikon DG-2 plus the appropriate eyepiece adapter.
It's out of stock but somebody must have one.

The D200 does that; just push the center button on the 5-way and it
jumps in.

The Mamiya magnifier needed a different eye position than I used for
viewing the whole screen, but it popped up very quickly.  And back
down quickly, too.

I usually need a hand under the lens for something like that, is that
the issue?  Since I can't compose on the LCD on my DSLR, I haven't
been using this technique much with the DSLR.  

Yep, that's longer than I use.  My normal strap puts the back of the
camera definitely above my navel.  I even thought of putting "adjust
strap length" somewhere in the instructions; it definitely needs the
strap in a particular length range.

In real night, I'm often scale-focusing.  My fastest is also an f/1.2
Nikon -- slightly bigger than yours though since the focal length is
58mm rather than 50mm.  

Well, it took quite a while to take over photography. My recollection is
that it wasn't until the late '50s that SLRs started to become really
popular, say 20+ years after the first Exakta. And it was still the absence
of parallax, and seeing the image as it was formed by the taking lens, that
eventually made it a success. It's worth remembering that some SLRs didn't
even have true lens interchangeability, long after the type became popular,
e.g. the Contaflex, the Retina Reflex and one or two others.

When I first became seriously interested in photography, in 1951, the Exakta
(and its cheaper cousin the Praktica) were not that highly regarded by most
35mm photographers. The Leica was the world standard, Contax having been
pretty much looted by the Soviets, Nikon and Canon were just beginning to
make names for themselves -- all rangefinders. I don't recall that the
Japanese even made an SLR at that time. The Exakta sold for about the same
as the Leica but was sniffed at by most. And while lens interchangeability
was of course important to some it was by no means something universally
desired. A friend's father had a Leica IIIf (I think), only had the 50mm
lens for it and had not the slightest interest in any more lenses. Cartier
Bresson used a Leica and almost always with the 50. I think lens
interchangeability only became important for the consumer market when cheap
lenses became available.

In order to use even moderately long lenses with a Leica you had to go to
one of those reflex housings, right? That couldn't have been much fun. All
because the camera couldn't show you the image formed by the lens.

Sure. I used RFs and TLRs for years myself, but I wouldn't say the parallax
problem wasn't troublesome -- it was just something most of us accepted and
had to live with until SLRs became available at reasonable prices. As you
say, the Leica (and most other RFs, and TLRs too) wouldn't focus much closer
than 3 feet -- which partly took care of the parallax problem, but at the
expense of eliminating closer subjects, unless you went to the bother of
using close-up lenses, and then you really couldn't see exactly what you
were going to get.

Beats me. I had a couple of Yashica-Mats but never a Mamiya.

No doubt it depends on what you want to do. As I recall, in the '60s and
'70s the TLR was pretty much the standard for wedding photographers, and I
suppose that for that kind of work it was perfectly satisfactory.

While I'll agree with that ;-), just about any question asked
by someone who is not familiar with a subject does not make them
stupid.  It only shows their lack of knowledge of the subject,
so their question is not stupid.  Many people do not know how a
camera works or why a particular design is the way it is.
That does not make them stupid.  They could be far smarter
than everyone in this newsgroup, but not knowledgeable about
this subject.  That is why people come here and ask questions.

One can say do a google search.  Well, sometimes google just delivers
crap or unrelated stuff that doesn't help answer the question.
Maybe someone didn't know enough of the key words to type
in the right ones to get to the right pages in the search engine.

Roger