Larry Tesler gave a fantastic talk at CHI for his Lifetime Practice award. He presented a summary of his work in helping to develop the modern GUI, and focused specifically on modeless interactions and cut-copy-paste. It was really fascinating listening to all of the subtle issues and design challenges in something that we now take for granted.
One example that really struck home was a description of how modes worked in Engelbart's NLS system. To delete a word, first you might hit "d" to put the system into delete mode. Then you might hit "w" to put it into select word mode. Then you could use the mouse to select the text you wanted. Then you would hit an accept button on the mouse to confirm the action. Compare this verb-noun approach to the noun-verb approach we use today, where we simply move the mouse to the right place, select the text (ie the noun), and then hit delete. Much simpler, less error-prone, and fewer clicks.
I also liked Larry's takeaways, which he would briefly mention at the end of a good story. The six he had were: