Apparently, the US Patent & Trademark Office recently granted the "slide-to-unlock" patent to Apple. This could potentially portend a slew of new lawsuits from Apple against Android manufacturers, especially since so many Android devices use this type of unlock system. It's important to note that this patent was actually applied for back in 2005, so it's not something Apple was being a sneaky about. Here's a tidbit from the patent,
A device with a touch-sensitive display may be unlocked via gestures performed on the touch-sensitive display. The device is unlocked if contact with the display corresponds to a predefined gesture for unlocking the device. The device displays one or more unlock images with respect to which the predefined gesture is to be performed in order to unlock the device. The performance of the predefined gesture with respect to the unlock image may include moving the unlock image to a predefined location and/or moving the unlock image along a predefined path. The device may also display visual cues of the predefined gesture on the touch screen to remind a user of the gesture. In addition, there is a need for sensory feedback to the user regarding progress towards satisfaction of a user input condition that is required for the transition to occur.
The folks credited for the invention are iOS chief, Scott Forstall and Apple engineers Imran Chaudhri, Bas Ording, Freddy Allen Anzures, Marcel Van Os, Stephen O. Lemay and Greg Christie. At this point, it is unknown as to whether the new unlock mechanism in Android 4.0/ICS will be impacted by this, but we will keep you informed as things develop.

Source: via 9to5Mac