Usage of the word "technically"

I like the Wiktionary definition which is "based on precise facts". Consider the following example:

I earn $9,000 per year and live comfortably, although technically I am below the poverty line.

"Technically" is used to introduce the contrasting observation that although the author considers herself well-off, she is in fact a pauper based on a precise definition of poverty. This use of "technically" to provide contrast seems typical.

I would not agree that "technically" and "literally" are interchangeable. "Literally" refers to the literal as opposed to figurative meaning of a word or phrase.

Many words and phrases originate in technical jargon, where they had meanings specific to the relevant field; later, they are often popularized in regular language, where their meaning changes into something more general, less specific to the field. We may then say that such an expression is used either technically/narrowly/strictly or broadly/generally/popularly.

Kate Moss is really obese: Chanel won't hire her any more. I mean, she isn't technically obese, since her Body Mass Index, the number doctors use to determine obesity, is still quite low; but that doesn't matter on the catwalk.

Since technical jargon is often more precise and detailed than other language, the phrase technically [speaking] is tending to develop a meaning identical to strictly speaking, as in your example. This in turn may sometimes even evolve into something closer to a general intensifier, like really.

This broader use of technically is resisted by some, who feel that it introduces another synonym of strictly that we hardly need, while rendering its original sense, as used in the relevant field, unusable. They advise that technically be reserved for expressions used in a sense specific to a certain field or profession, as opposed to cases where strictly would do.

Literally means non-figuratively, non-metaphorically: if you mean something literally, you say it in such a way as to exclude anything but the simple interpretation, if several interpretations are possible.

I am literally burdened by my large breasts: their weight hurts my back. I am also figuratively/non-literally burdened, because I don't feel free to wear any shirt I like because of them.

This word too is now often used to mean something like strictly speaking, and even as a general intensifier, which is strongly discouraged by many style guides.

If you describe something as technical, you're suggesting there are many detailed aspects and implying that perhaps it isn't reasonable to go into so much depth. So following this logic, technically is stating that something, as a result of many detailed aspects, would shed light in a different manner, usually contrary to what has been said previously as if to demonstrate a point.

In other words, you could replace technically with "If we went into more detail, you'd find that the following is true..."

Other answers seem to cover a broader scope than the question actually requires.

In the common expression technically speaking, the precise meaning of technical isn't really the issue.

I could have preceded the above sentence with Technically speaking, - it would still be grammatically and semantically valid, even if it looked a bit odd.

That's because Technically speaking,... is an idiom (cliche, IMHO) that effectively means something like Bearing in mind some minor point of fact which I happen to know [and you either don't know or are ignoring],...