JayFreeman, aka Saurik, the founder of Cydia, the app store for jailbroken iOS devices, said in a 2011 interview that the share has historically been around 10%.
In the six weeks since evasi0n was released, however, close to 18 million devices have already been jailbroken, according to data from JayFreeman, the administrator of the Cydia app store for jailbroken devices.