"If you were trying to imply that Q is the energy added to the system that the light is being focused upon,"
No, I'm guessing Q would be the heat added to the magnifying glass on the sun side, which is very small compared to the heat produced on the side where the light is focused; the latter heat does the work you want (lighting a fire or whatever). Since Q is small, and W is large, U should be negative. But it's not.
"The process of compressing your data costs more than decompressing it. Rule of thumb holds."
Costs more in what sense? Energy cost? Lines of code cost? Time cost? In any event, it is not something that I consider when zipping a file. Zip and unzip are treated as equivalent from the user's standpoint.
"A magnifying glass, simply put, directs the energy that hits its outside lens surface to a much smaller area, at the cost of the loss due to diffraction of light."
The point that confuses me is: the energy on the outside lens surface can't light a fire, but the energy produced by the glass can. What work was done on the outside energy? It was redirected inside the lens, but how is that work? Doesn't work in thermodynamics reduce to the lifting of a mass in a gravitational field? How is the lens doing any work, in that sense?