Yes, the obvious answer is "right there, on my handlebars, where else?"
But you see, I've moved a few times in the last couple of years, and each time my organizational scheme seems to fall apart somewhere, and as a result, I don't know where most of mine are! As regular readers, friends, family and my staff knows, I own a LOT of bikes... and most of them have the wheel magnets, pickups, and wiring harnesses of some sort of bike computer attached to them. But at the moment, I have no clue where most of the main computer units are for most of my bikes! Somewhere there's a box...
So, as a result, most of my rides lately have been of indeterminate time, speed, and distance. And you know what? I don't mind that at all. There was a time it probably would have bugged me, when I carefully logged all of my miles, and average speed, with notes about the weather and type of ride (commuting, group, solo, casual, fast, etc.). Nowadays, it just doesn't seem as important to me... I'm out there just to have a good time. I'm slower than lots of folks, and faster than some, and that's fine with me. I don't need to know the specifics all the time.
That's not to say I'm going to throw out all my computers when I do find them... I'm just not in a panic about finding them, and doubt that I'll be very consistent at tracking my stats when I do find them. It's all about the fun, you know?
Community Cycling Center in Portland, OR. Mostly original, and a classy looking bike, no?