Sony surprised with the invitation to a PlayStation media event that is happening tonight at 6pm. It is kind of an odd timing. Sony did not specifically say that they will unveil the Sony PS4, but everything points towards such an announcement.
It will though likely be a big tease for the PlayStation 4 without much real hard-core information. We for sure will not hear anything about the price and we also will likely not hear about the hardware specs. Sony might reveal the major new things like game streaming, smartphone/tablet integration and the new touchscreen controller.
Overall though I expect that we will be left behind after the PS4 event with tons of question. I suppose this is Sony's intention. They want to ignite the conversation about the PS4 to drive up anticipation and chip away on the hype Microsoft will get for the Xbox 720 reveal this year.