Earlier today, I wanted to start a large download on my home machine. I normally do this via SSH and then the 'wget' (or 'curl') command. However, this particular page was using a PHP submission form, and I just could not get it to work in curl or wget (probably user error!). So I launched 'links', the text-mode browser instead. This worked fine, and the file began downloading.
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:
Mac OS X Hints
http://hints.macworld.com/article.php?story=20011116132016557