Surprisingly, given that it was the hottest day of the year so far here, it wasn't super-amazingly hot inside.
When I got in, just after 4 PM, it was 24C downstairs and 29C upstairs - it was 31C outside, so aside from the windows for the air-con hose there was no need to open windows. It's now 29C outside, 24.5C downstairs, 33C in the back bedroom and a much more pleasant 22C in my bedroom.
There are two things worth noting:
One, it shows how much of a difference new windows make. Last year it would have been pushing 38C upstairs and 30C downstairs on a day like this, but this year the improved insulation has worked to keep the heat out.
Two, it shows how many people lack common sense - most of the houses round here have windows open as wide as they go, which is a great way of getting all that 30+C air into the house. They'd be better off keeping them closed until the air temperature drops below the indoor temperature, but it's too late now!