Hi folks.
Also, if you read the message in the status bar after selecting the Smoove Tool, you will read: Click to select the base point of the smoove or type a new radius for the smoove.
Also, the Measurement Window is labelled Radius with a value in it.
Not to mention this page that I found using the Help Menu:
http://help.sketchup.com/en/search/sketchup/smoove%20tool
Just ideas.