I got in this morning at my normal time (9:20 ish) to find the office already full of people who do not usually arrive until nearer 10. I asked if everyone had forgotten to put their clocks back, or if I'd put mine back twice, while waiting for the claxon (I had read this post at home before I left for work!).

Of course, it's perfectly possible that a fair number of people will show up early the day after the clocks change, not because they forgot about it but just because their body clocks haven't adjusted yet and that's when they naturally happen to wake up.

(Indeed, that includes me. I didn't deliberately arrange to come in an hour early today; I just happened to be awake, and it occurred to me that since I was leaving early this afternoon it wouldn't be a bad idea to use the time this way.)

Absolutely. In fact I think in this case there were a couple of people in that boat, a couple who had decided to switch their working hours from 10-6 to 9-5 to coincide more with the remnants of the daylight, and one who had been sleeping elsewhere the previous night and hence made it in earlier than usual.