Since it was a large file, and I had other things to do in the Terminal, I minimized the window to the dock. My machine immediately became very very slow and hard to use. I managed to get a "top -u 10" launched in my Terminal, and noticed that the Dock was using 70% of my CPU!
So I killed the dock process, thinking it had taken off for no good reason. The dock restarted, my minimized window came forward, and all was back to normal. Thinking things were OK now, I minimized the window again, only to have the same problem occur - completely unusable machine.
A little experimentation led me to the cause of the problem. Docked Terminal windows, at least as of 10.1.1 (probably 10.1, too, but I never checked) now "live update" their content in the dock! The 'links' program has a screen display that shows estimated download time remaining, and it updates in real time. So my dock was continuously trying to update that miniaturized window (over a remote connection, no less). Not a good situation! I'm not sure there's a workaround, other than what I did -- drag most of the window off the screen.
If you'd like to see the impact on your machine, read the rest of this article for a simple experiment you can run...
Docked Terminal window experiment:
- Set your dock to visible and max size (just so you can see what's happening)
- Open the Terminal
- Type cd ~/Library/Preferences (so we have a nice long directory to work with)) and then repeat 25 ls -al. If 25 isn't enough time, use a bigger number.
- Hit the minimize button.
- Notice the nifty directory listing flowing in the dock.
- Notice that your machine is quite slow - try clicking on other dock applications, for example, or even try to un-minimize the window.

