but I reckon I can spot someone who is interested in getting training/exercise by their cadence
That's even more interesting...? Is there a linear corellation between cadence and commuting:training ratio?!
I ride without a bag, because I hate riding with luggage, still commuting!
I don't insist on racing, but if I'm starting in front of cars, I'd rather stomp and get out of the way, rather than dither around trying to work out whether someone's quicker than me, but slow off the line because they're SS, not clipped in, didn't change gear before the lights, or just slower. I'll stomp, get round and in, if you want to overtake down the road, go for it.
Makes sense, but you get people (in London at least) who are out of the saddle screaming away from every set of lights like their life depends on it. They stand at the lights panting and pouring sweat, looking at you out of the corner of their eye to see if you're 'taking the bait' as it were. Doesn't annoy me, I save racing for when I've got a number board on, it's just amusing.
What does annoy me is people who wobble to the far right hand side of a queue of riders at lights (which can often be 20+ bikes in London), then set off really slowly, and wobble back over to the kerb. If you can't get away at a decent pace stay to the left FFS!