The acorn is a symbol of patience and an old English proverb states that "Great oaks from little acorns grow," referring to the fruition or completion of an idea or task.
In old Norse legends, the mighty Thor sheltered from a thunderstorm under an oak tree. This has given rise to the belief that placing an acorn on the window sill will prevent lightning from striking the house. This is also why you will often see window blind pulls shaped as acorns.
After a bit of research, I also discovered that acorns can be turned into whistles! Visit the Science Toymaker site to see how it's done.