Randy,
You are absolutely correct. You want to draw the cold air off the floor whenever possible - especially in the basement. Quantity and location depends on a number of factors.
How "chopped up" is the basement? How many rooms are there? Any going to be used as bedrooms? Is there a door at the top of the stairs? Any supplemental heat? (Gas/Wood/Propane fireplace? / electric baseboard heaters?)
In some situations, you have no choice but to install it at the ceiling. Just remember it will be drawing the WARM air off the ceiling. If you find it is making the room less comfortable, it is always easier to block it off, than trying to install one after the room is finished.
Shawn
