Well.... I work for an IT consultancy firm and our job is usually to forecast technology leap. For fun at work, here's what a consultant predicted:

PS4 Specs: 

Launch Date: July 2013
CPU: Cell Broadband Engine with 32 Cores (well, that really depends, he's thinking it's gonna be pretty cheap compared to the price of the current CBE when it came out)

RAM: 8 GB Graphics:

RSX GDR 2GB HDD: 4TB or 1TB SSD

OPTICAL Drive: Blu-ray (probably 400+ GB capactity)

VI: PS Eye 2.x

Controller: PS Wand / DS4

The actual launch price of the PS4 will be $399 - $499 depending on bundle and features. Both Version will include PS Eye and Controller. Surprisingly, if the PS4 does come out in 2013, the PS3 would phase out in 2015 in line with Sony 10 year plan. The PS3 is now over 3 years old.

On a side note, he claims that Natal will be huge but only with the X-Tri (His code name for the next Xbox - Which I think is catchy and MS will jump on)

Retail availability: November 2013

Cpu: Cell with either 32 or 64 SPEs and 4 or 8 PPE (IBM is going to unveil a 32 spe, 4 PPE improved cell cpu in 2010), fully compatible with latest opencl / GPGPU standards.

Ram: 8 - 16 GB. 

GPU: A multi-core cGpu that can do GPGPU programming with relative ease. It will be a monster of a GPU, capable of 10+ teraflops (in 2011 both AMD and Nvidia will have launched cGPUs capable of 5-7 teraflops), considering also that both the xbox 360 and the ps3 have gpus that have year 2005 tech.

Fast Blue-ray player that supports 400-1TB blue-ray disks (it's a fast evolving medium), 500gb-1TB HDD

Natal like camera, Motion controller improved over the Wii (people are joking if they believe that they will be able to play games with relative ease with nothing to hold on to. Expect player input to be a hybrid between natal, wii like controller, and DS4).

Expect its graphics to boast a hybrid approach between raytracing and rasterization, with real-time and ingame physics like nothing shown before (fully malleable and natural environment).

Launch price: 499 USD (keep in mind of inflation). They need to differentiate themselves from the Wii 2, which will probably be launched by mid-end 2012, and whose tech will still be impressive (consider how the gamecube was launched in 2001 for 299usd and was slightly more powerful than the PS2 - expect the Wii 2 to be much more powerful than the PS3, whose tech is of the year 2005), and whose cost will be 299usd.

Sony boasts First party developers that Microsoft and Nintendo do not have. Nintendo is unfortunately sleeping on its own success and relies too much on Shigeru Miyamoto - they are cash-flow rich and should have focused on the side on creating new first party studios at Kyoto, yet they are not doing that. I am not saying that Nintendo is going to go downhill, but I am worried that they are not as proactive as one should expect them to be. 

For example, why is it that a producer of Fumito Ueda's calibre had to work for Sony? Why is it that Nintendo has not focused on gathering talent like him? Nintendo is composed of extremely talented people - they would not have much of a problem in gathering talent such as him, and yet they are not doing that. They are so cash (7bln dollars in the bank) and cash-flow rich that they would have no problem in funding 300mln usd worth of projects a year of talented studios such that of Ueda (what is important to keep in mind is that the success of a game does not depend on the amount of money invested - studios such as that of Ueda do well on a 10-15 mln dollar budget, working at a moderate pace of one game that cost 10-15mln usd to produce every 4 years). Nintendo would be able to produce a substantial profit from funding talented studios such as these, consdering too that they have no royalty fee to pay for, and can thus derive a profit of 20-30usd per copy of game sold at 50-60usd.

Microsoft to me is not faring that well. I don't have time to go indepth, but consider the fact that they do not really have valuable first party studios (even though what is important to note is that even the God of War studio was not considered that valuable before they released GoW 1 - this is especially noteworthy given that Micrososft acquired Rare studios for almost 300mln dollars and so far they have not produced anything noteworthy for the xbox 360, which is again why I was saying that money does not buy talent, only talent can gather talent, and this is why Nintendo is in a much better position than both Sony and M$, given the quality of the the talent that work at nintendo). Natal is not based on tech unique to microsoft - Nintendo and Sony are going to easily replicate it (there are many companies that are stating that will be able to provide tech / hardware similar to that of natal at a good price point in one or two years). Indeed, last I heard, Natal was based on tech not only derived from that company that M$ acquired, but also from other similar companies (can't remember their names) who are able to provide the same tech to competing companies such as nintendo and sony.