I know that Wikipedia isn't an academic source, but this explanation seems right to me, based on my experiences in both the academic and private worlds:
"In written English, the symbol K is often used informally to mean a multiple of thousand in many contexts. For example, one may talk of a 40K salary (40000), or call the Year 2000 problem the Y2K problem. In these cases an uppercase K is often used. This informal postfix is read or spoken as "thousand" or "grand", or just "k", but never "kilo" (despite that being the origin of the letter)."
They also mention non-standard usage:
"Metric prefixes are widely used outside the system of metric units. Common examples include the megabyte and the decibel. Metric prefixes rarely appear with imperial or US units except in some special cases (e.g., microinch, kilofoot, kilopound or 'kip'). They are also used with other specialized units used in particular fields (e.g., megaelectronvolt, gigaparsec, millibarn). They are also occasionally used with currency units (e.g., gigadollar), mainly by people who are familiar with the prefixes from scientific usage."
Note, however, that these instances of non-standard usage are emulating traditional SI usage in that the prefix is prepended to a unit of measure. I suppose that you might argue that "troop" is a unit of measure, but then the labels would say "19.2 kT" for "19.2 kilotroops", or 19200. That sounds silly, to me.
As for binary, the correct prefix for 1024 is Ki. Yes, with a capital K. For instance, 1024 bytes is 1 KiB, or one kibibyte.
K is a binary prefix, while k is the mathematical use of 1.000 borrowed from the greek word which means thousand. KB means 1024 bytes, but kB would be 1.000, since the k relates only to 1/1000 not only to the metric system... but you could also look it up 
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