I don't know if there are comparable Windows and Mac equivalents, but with Ubuntu I have this nice "Gnome system monitor" that shows me CPU, Memory, Network, Load Average and Disk IO usage % in real-time at all times. I can't imagine living without it.

There's no way I couldn't notice something taking 100% CPU for a long time while not writing to disk when it ought to start writing to disk immediately.

It's part of the reason I notice and hate flash stuff that takes 100% CPU for no reason at all. (but I'd notice anyway because my fan gets noisier real fast)