The concrete made it into the forms just in time before the skies opened up and dumped buckets. This would have been disastrous had it been flatwork, but all it did to the stem walls was give a mild exposed aggregate finish on the very top of the walls.
The pour got off to a shaky start - I arrived as the truck was backing up, and had to literally stop the truck as concrete started down the chute. Got the guys to fix a few problem areas - rebar in the dirt instead of suspended up where it would be encased. 5 minutes later and we'd have never known - until problems occurred (or... not) years down the road.
Being able to keep a closer than normal eye on things has been a great advantage. My guys are really quite good, and care about their work - but even they miss things or think "good enough". Having an extra set of eyes around is important. I shudder to think of what goes on at the houses that get built with bottom-end contractors and no construction observation by the architect.