The Notebook page is still very basic.

A issue that always confuses me and resulted in data loss today:

How to I quit a notebook saving my work?

File -> Close and Halt
==> Kernel apparently stopped and all data lost!

File -> Save
==> Work saves but notebook still active.

What I miss:

File -> Exit (halt) saving changes.

Or better:
When I exit (halt) a pop-up:
"Do you want to save or discard the changes.