Use MacVim as standard Terminal? I used to love the terminal.app for many reasons.

I especially liked the way I could navigate to a file and edit using vim it all in one app, without having to leave the keyboard. 

But, since the terminal.app doesn't support many of vim's rich features, I decided to make the step to MacVim. 

This breaks the symmetry though, I have to use terminal.app to navigate to a file, edit in MacVim (using mvim of course), quit MacVim and open up the terminal again. 

Isn't there a way to use MacVim in stead of terminal to do all this? I'm not talking about iTerm 2 etc, these apps don't cut is for me. I'm talking about true unix command line in MacVim.. 

This should be possible, I guess, only... is it?
You're confusing the terminal with the text editor, as other commenters have pointed out. Still, there are a number of ways to make the terminal more vim-like, or vim more terminal-like.

If it's vi-style keybindings in the terminal you're after, add set -o vi to your ~/.bash_profile (assuming you're using bash). This will allow you to use vi-style keybindings at the command line (hjkl movement, modal editing, etc.)

If you just want to be able to execute unix commands from within vim, prepend ! to the beginning of those commands at the (Mac)Vim command line. For example :!pwd will print the working directory.

There are also plugins like Conque which allow you to run a shell from within Vim, which sounds like it may be exactly what you're after.