We have all heard the admonitions to dispose of remaining brake fluid once we are done with the open can, but check out this recent post on alt.autos.gm:
Picked up a bottle of brake fluid off a shelf in the gargage yesterday and heard a funny noise. There were three little balls of ice floating around in there.
Never seen that before.
This was left over fluid from September 2004 when I changed front brake hoses on the Bonneville.