It’s the little things. This just got added to my bookmarks; maybe it’ll be on yours.
Press the spacebar repeatedly, and you get an accurate BPM count for a song. It’s actually useful to help learn to recognize BPM, as well, if you listen frequently when at your computer. (The trick used to be to look at the second hand of your wristwatch, as two ticks would be 120 bpm – but that requires an analog wristwatch.)
And yes, surely this will be one of the first native Apple Watch tools when its native SDK ships next year.