(Quad posting, I know)
On the PS4 hardware: CPU wise, looks like Jaguar, as suspected. 8-cores, undetermined clocks (probably about 1.6 GHz or so). IPC will determine if this is a net gain over the Cell or not (would have to have about 2x the IPC of PCC, which is about what X86 gets), though the ease of coding over Cell will likely net a bit extra increase. Its a better CPU, but not a huge leap in performance.
On the GPU, thats where 90% of the performance is. Looks like performance roughly equivalent to a 7850/7970. So at least 4x the power of the PS3 GPU (modified 7800GTX).
The 8GB GDDR5 RAM is shared between the system and GPU. This is a good thing in some regards (CPU has direct access to the GPU framebuffer this way), but I worry about CPU latency compared to DDR3 (GDDR tends to have high bandwidth, low latency. DDR is the opposite). This could end up being a significant limiting factor, as memory reads/writes are going to be costly. As it doesn't appear the PS4 will support task switching like the 720, its likely all that RAM (or at least a good sized chunk of it) will be free for developer use, so the per-application RAM limit should be higher then the 720.
My major concern, again, is that the closer to PC hardware will lead devs to not take advantage of the fact they can code very close to metal, and lose a lot of performance as a result.