I have vim-mode-plus installed on atom, however I can't execute commands like ":w" or ":wq" etc.
I believe the mode is called "ex mode". However I thought "semi colon mode" may translate better for some beginning vimmers (vimmers == vim users).
You need to install another atom package called "ex-mode".
This restores most of vim's functionality. The packages ex-mode and vim-mode-plus has made it so that I don't see much difference in functionality between Atom and vim. This being said, my experience with vim hasn't been for long and hasn't been as in depth as others.
Note: I found this simple answer hard to google, so I posted this question + answer.