Since the most common reason for mis-use of these prefixes is
typographical errors, information on correct usage will only go so
far.  And teasing or flaming people who mis-use them when the
intent is clear is not helpful. FWIW, here is what I know about the
official and unofficial correct usage for SI prefixes.

In the United States, the National Institute of Standards and
Technology (of the US Dept or Commerce) is the standards body
for correct use of the SI.  URL is www.nist.doc.gov
Their Special Publication 811 describes the acceptable use of SI
and the prefixes, as far as spelling, use of units, use of the prefixes,
etc.  It specifically says that using "kilo-" (abbreviation K) for "times
1024" is unacceptable, and using "mega-" (abbreviation M) for
"times 1048576" is unacceptable.  So strictly speaking, none of the
examples Brent asked about are correct.

In the SI:
small k is kilo, means x1000;
large K is a unit, the Kelvin, not a prefix;
small m is milli, means x 1/1000;
large M is Mega, means x1,000,000;

That said, everyone in the computer industry ignores this official
doctrine and uses the SI prefixes anyhow.  This does lead to
confusion sometimes. But I think this usage is too entrenched and
convenient to abandon it now.  There is a convention that seems to
be used consistantly in technical papers and the computer trade
press that the unit "bit" is abbreviated "b" and "byte" is abbreviated
"B", but this has no official standing that I know of.  So the examples
Brent gave do comply with this unofficial "standard".

A set of acceptable prefixes to use for the binary multipliers was
proposed not long ago.  It proposed to use a "b" (for "binary") to
qualify the prefix as being one of the binary multipliers.  So 1024
bytes is supposed to be abbreviated "kbB" and (wait- here's where it
gets even more silly-) pronounced "kibby-byte".  Similarly, MbB
("Mibby-Byte").  I had to check carefully to see if this was an April
fools joke or a hoax.  It isn't.  Well, I think that horse left the barn in
the 1960s, NIST can close the barn door if they want.

That's my 2 centidollars.

Barry.
------------
Barry King, KA1NLH
Engineering Manager
NRG Systems "Measuring the Wind's Energy"
Hinesburg, Vermont, USA
www.nrgsystems.com