Well, I though I'd give this a go today for the first time, so signed up, downloaded the app for my phone and logged in.
At the start of my ride, pressed "Record a ride", waited for gps lock, display set itself from dashes to zeros and off I went, hell for leather on the segments I wanted a bash at. Got back completely knackered only to find I'd recorded naff-all.
It turns out that the (unlabelled) roundel button on the screen was the Start button and not, as I assumed (having already pressed "Record a ride") the Stop button. Doh!