There are times when you're moving a slider across a big range but with lots of small steps and it's difficult, if possible, to select a precise value. Imagine two values are only 1px apart, or even sharing the same pixel position. Here's an idea. We could enable the user to hold down the Ctrl-key (Option-key on a Mac) while dragging a slider handle and the effect of the same movement of the mouse would be slowed down 5-10 times. So you could really dial in between a couple numbers that are really close together. This idea comes to me from some Adobe Creative Suite controls that have this behavior and also this thread:

http://forum.jquery.com/topic/using-slider-with-times