CES 2012: We RumorTT'd about this a few days ago, but speaking at a "roundtable with reporters" at CES, Sony's Kaz Hirai answered a question about the possibility of the PlayStation 4 being shown off at E3 later this year. Hirai said:

Andy (House) is absolutely right in that we are not making any announcements at E3. I've always said a 10-year life cycle for PS3, and there is no reason to go away from that.
Now, I'd like to go on record and call BS on this statement of a "10-year cycle", and at least bet we'll see a PS4 before the PS3 has been out for 10 years. Also, wouldn't it be perfect to pretend to let your guard down "hey guys, we're not teasing the PS4 at E3", while Sony are sitting there waiting for Microsoft to either unveil a new console, or hold off expecting Sony to not have anything.
Not only are new consoles needed because the current-gen consoles are ageing (we're in a Full HD era playing sub-HD games at sub-30fps), but Nintendo will catch up and even surpass them in terms of technological capabilities when the Wii U launches. What a slap in the face to the "HD gaming era" we supposedly entered. Sony and Microsoft need less than 5-year cycles, considering the tech pace smartphones and tablets are jumping at.
I guess we'll have to wait and see.