Not in any production workloads. They do work these days in PyPy though, so I'd feel comfortable doing so if we did, although I'd probably feel just as comfort

Not in any production workloads. They do work these days in PyPy though, so I'd feel comfortable doing so if we did, although I'd probably feel just as comfortable writing whatever numerics in pure-Python too unless it was stuff that already existed easily elsewhere. On a personal note I've played with OpenCV as well (and done so with PyPy to do some real-time facial analysis on a video stream), but yeah also not for $PRODUCTION_WORK.