It would be extremely helpful if the Output Log (command line) window of Workbench had a built-in command history, one which could be run through using the up arrow key.
This is a usability feature that is common place for both the Linux and Windows community, and for most other command line communities (Matlab, R, Octave, etc.). This is the way most console / shells work.
See for example: http://en.wikipedia.org/wiki/Command_history
Use Case 1
Often, getting a command right with all of the right options is a bit of an iterative process. You type something in, either there's a minor typo, or you forgot a required option. So the command doesn't run or there's an error message. It is somewhat of an annoyance to have to re-type the entire thing. Up-arrow is what you'd expect (instead of having the cursor scroll up.)
Use Case 2
Many commands in hg produce lengthy output. E.g. hg status. This wipes out what you may have done two or three commands back. Being able to up-arrow and scroll through history would be an easy way of recalling what you did.
Bug (not enhancement)?
I'm tempted to call this a usability BUG instead of an enhancement. Certainly, no mature command line interfaces that I've seen (except extremely primitive / defective ones) have been without a command line history...