I'm no UEX expert..

Then let me enlighten you. Your ctrl-alt-delete example is poor due to the fact and this is backed up by a Bill Gates interview that that command was meant for debugging and was not supposed to ship in the final product. People started using it and they had to leave it in.

Some music players do not use space for pause/resume.

As for clicking and zooming, these things are so intuitive that children can learn on their own how to do these simple tasks. OLPC and other organizations air drop laptops into Africa and people who have never a seen a computer get them and teach themselves how to use it and how to read.