This is quite neat. I tend to just fire up the Python or GNU Units whenever I need some quick math, but it's nice to have something rather consolidated.
I used to use Lua for quick calculations, but I've recently started using R because of operator vectorization.
For conversions, why use GNU Units over, say, Google in your browser? I find that most of my unit conversions happen in my browser, while I'm online. Anecdotal evidence, obviously, but is this not the case for others? Where do most people use unit conversions?
I'm also not an engineer, so I can't take that into account from experience alone. Wouldn't your tooling provide automated conversions into "correct" units?
Oh, I just use Units because I'm used to it, and it has always done the job well. I also like that it's self-contained on my computer, instead of requiring a dependency on the outside world.
