Hence the phrase: "f8 and be there..."

It's part right.  The real deal is that for most lenses, peak sharpness begins
at about 2 to 3 stops closed from max aperture.  So the story is slightly
different for an f/1.4 lens v. an f/3.5 lens or a zoom that starts at f/5.6.
Most lenses are fairly sharp through about f/16.

OTOH, if you don't use a tripod, it is all a very moot point.

It's not a bad rule of thumb to assume f/8 and the differences between f/8, f/11
and f/16 in sharpness are not very discernible in an image that is worth pondering.

There are diffraction limited lenses that are sharp at their widest apertures
and remain sharp for 4 or 5 stops down from there before becoming softer due to
difraction at very small apertures.

Having said all that, composition is usually more important than sharpness, so
choose the aperture for the composition.

Cheers,
Alan

Hmmmm ... I am just as surprised as you. If you have a perfect
circular aperture, then the diffraction is very easy to calculate.
So - thats not a problem. But - it sounds very strange that the
unsharpness due to lens faults should follow some kind of curve
that is similar for different lenses. Are you sure that it is not
first of April? :)

/Roland

For crummy, cheap regular lenses, stopping down always improves
sharpness.  This is a shame in a way because the larger the aperture
of the lens, the more true resolution it should have.  
The diffraction limit, which imposes the limit on detail seen is
roughly 4.48 arc seconds (smallest detail resolvable) per inch of
lens aperture.  So a 1" lens can show detail 4.48 arc seconds across
a 2" wide lens will show detail half that size, 2.24" across, etc.
For instance, given the same quality, a lens with a 4" wide aperture
should yield details twice as small as a lens of 2" aperture.
However, this only applies to lenses with enough focal length to take
advantage of the resolution afforded by aperture.  This would
(unfortunately) mean having a focal length = 2500mm for a 4" aperture
lens or 1200mm for a lens with a 2" maximum aperture.  This is one way
to reach the diffraction limit for a lens.  The only way to provide
that kind of focal lenght for those aperture is to use a telescope
which consists of a "prime" lens (called the objective) and a series
of positive lenses interposed between the camera the the prime lens.  
Camera lenses are not designed to approach the diffraction limit, none
of them are made to a high enough standard (1.8th wave accurate or so)
to get to the diffraction limit.  However, there have been
(apparently) camera lenses designed to provide maximum sharpness when
at full aperture, some of the "Noct" lenses from Nikon or Leica are
such lenses.  However, I don't know if the claims for their sharpness
are true or not.  
But getting back to the original concept of stopping a lens down.
Suppose you stop a lens with a 2" wide front lens down to f8.  That
means that the focal length versus the aperture is now 8:1.  For
a 100mm prime lens with a 2" (50mm) front lens, this means the lens
opening is only 12.5mm across and it's theoretical maximum resolution
is now only 9 arc seconds, far less than if the original 2" aperture
could be used.  What you have done by stopping the lens down is
minimize the inherent aberrations in that lens.  Sperical aberration
(the inability to focus light entering different areas of the front
lens to the same point) chromatic aberration, astigmatism, coma, etc.
This means that the residual aberrations of the camera lens (on
average) are so bad that you must drastically reduce the aperture to
obtain maximum sharpness.  However, because of the limit on focal
length verus aperture in a camera lens, the lens's true resolving
power (even at a small 12.5mm aperture) is never reached.
-Rich
-Rich

It does. A good lens is best at much larger openings.

And this part of the article shows me it's BS..

"The 50/1,8 lens was focused using the cameras superb auto-focus."

You NEVER use auto focus for lens testing.

Bottom line, test your own lenses. Some medium format lenses need to be
stopped down to f11 to be "their best" some of the newest digital lenes are
best at f4.

I think it depends on the lens.  I've used my 85 1.8 to take some awesome
and very sharp 35mm photos taking advantage of the limited depth of field
the lens provides.  Looking forward to getting my new D70 and using the lens
with it.  The only thing I'll miss is the up-close-and-personal touch the 85
gave me when I used it for portraits.  I'll have to back up a bit due to the
magnification factor.

Isn't DoF also an issue? I mean at wider apertures you have shallow DoF
making it difficult to focus accurately as I discovered with a Pentax
Super-Takumar 50mm f/1.4.

The limited testing I did with my Canon dRebel kit lens and the pentax
lens told me the same thing as the photodo test - that the lens is
sharpest from f8-f11. From then on, given enough light I use the lenses
at f8.

- Siddhartha