Those of you on the fence, if system performance/power means anything to you, consider this. These 2 systems are NOT similar in specification. First of all, it needs to be said that there is a considerable difference in the GPUs in these machines. Not only does the PS4 have a 50% raw output performance advantage between the two, but it is architecturally identical to a GPU that one would find in an APU-based desktop or laptop. This allows developers familiar with those tool-sets to have their performance out of the gpu a known quantity. For the PS4, this is a win-win over the XBox One because the difference doesn't just stop with having the clearly superior graphics processor. The fact that there is no EsRam for developers to have to code around means that there is little uncertainty about graphics budget or debugging. Setting up an engine to run on the thing is not time consuming.
Second off, we don't know a lot about the underlying architecture of the CPU in the XBox One, but we do know that Sony has put in some interesting goodies in the APU in PS4. It features a memory store rather similar to what was used in Cell for starters and has some other proprietary tweaks that put some gap in closed-system functionality from the typical APU you would find in a laptop. The clock speed of this part is known and Mark Cerny (lead architect of the system) has gone to some length to explain how some of these features were implemented to give developers some long-term headroom for getting high performance from the part.
Third, and most importantly, the system bandwidth differences between the two are enormous. Perhaps, some people beat the DDR5 drum a bit without know what it really means, but what it does mean for developers is that they can keep the system fed with data and not have to fall back on a lot of trickery to make it happen. The XBox one is using DDR3, which if you remember, is the same memory the XBox 360 used. In this aspect, there has been very little progress technologically from current/last gen and to facilitate that weakness, memory move units have been put in place. It's still not an adequate replacement for raw performance. No developer would tell you otherwise.