Found this interesting video of the Sony Aibo, an electronic pet "dog" marketed by Sony a few years back.
Unlike the maker of the video, I just don't think it would be as much fun as a cat.
Robot pets are a big industry in Japan; they're seen as convenient companions for the elderly or in situations where there's not much space in small apartment buildings.
Here's two ads for a Japanese robot cat:
And a video that shows a robotic pet seal named Paro. There's also another video on YouTube showing it interacting with patients in a Japanese nursing home.