As a lot of people have said, the actual inclination is just one factor… 45 degree in nice powder with a nice safe run out and no rocks is pretty good fun. 30 degree on ice and/or with rocks and/or with a cliff at the bottom etc is potentially much more serious.
To answer the initial question, I think the steepest I’ve skied is about 47 degrees. This was the average gradient and was in very good snow - I know the top was much steeper (well, vertical for about 4 metres:-) ), so most of the actual turning was probably on 45 degrees or less. I tend not to worry too much about how steep something is, I guess I’ve finally grown out of that:-) (perhaps my hip surgery influenced that too, but thats another story). I’m much more concerned about avalanche risk, finding nice snow, having fun and getting down in one piece these days.