I think you are overstating the constraints.  Instead of 512 unified it's 256 and 256, it's not like NONE of the 360's 512 is going to the CPU.  I'd guess (and I admit it's a guess) it only feels like a "straitjacket" to those who carelessly wrote for the 360 without even considering that they would have to port it to the PS3 later.  Cry moar, I'm sure there are some problems if people do the opposite as well. 

Anyway, back when this debate was raging originally, I'd gotten the impression that the Cell processor (with its kind-of-independent SPUs) was the biggest problem going from 360 to PS3.  Not so, or not anymore? 

I believe that most of the learning curve regarding the Cell has been understood and adopted into Modern Game Engines. Its still a bit of a pain and its hard to extract every last bit of power but the Cell is powerful enough to match strides with the more conventional architectures.

The big problem now is indeed the memory constraints on the PS3. 256 MB is simply way too small for graphics nowadays. Imagine being a multiplat developer applying textures to your game on the PC dev kit (They nearly all are for multiplat) and constantly having a PS3 Texture limit reached warning crop up.

I honestly think the PS3 is a great machine held back by some terrible design choices. I expect the PS4 to have all these problems rectified.

OK, but how much of the 360's memory (over 256) can really be counted on?  (Honest question -- I'm curious and don't know.)  It's not like the CPU doesn't take any.  Definitely there is advantage to the 360 there, but it's not like the 360's memory is impressive compared to PC memory either. 

I believe that most of the learning curve regarding the Cell has been understood and adopted into Modern Game Engines. Its still a bit of a pain and its hard to extract every last bit of power but the Cell is powerful enough to match strides with the more conventional architectures.

The big problem now is indeed the memory constraints on the PS3. 256 MB is simply way too small for graphics nowadays. Imagine being a multiplat developer applying textures to your game on the PC dev kit (They nearly all are for multiplat) and constantly having a PS3 Texture limit reached warning crop up.

I honestly think the PS3 is a great machine held back by some terrible design choices. I expect the PS4 to have all these problems rectified.

OK, but how much of the 360's memory (over 256) can really be counted on?  (Honest question -- I'm curious and don't know.)  It's not like the CPU doesn't take any.  Definitely there is advantage to the 360 there, but it's not like the 360's memory is impressive compared to PC memory either. 

as much as the developer wants to allocate rather than being constrained to up to 256 for CPU and 256 for GPU* like the PS3, on the 360 if the developer wants to allocate 400MB to graphics then they can do that as long as they don't need the memory for something else and if the game needs more for CPU tasks then they can do that as well and the changes can can be made on the fly as well so if one level needs extra textures but has less physics then the system can do that. Which is one of the reasons why the 360 is easier to develop on.

* On the PS3 it is actually possible for the Cell to access VRAM and the GPU to access main RAM so devs can use the CELL for rendering tasks but it incurs a performance penalty from what I have read.

Fair Question....without a perfectly clear answer.

It ultimately depends what you are using the CPU for.....Complex recursive algorithms found in most games you may not be able to borrow too much.

However it provides flexability.

For instance people have often been amazed that the textures on the Xbox are so good given the restrictions of DVD size.

Say hello to clever use of the 360 memory to decompress textures on the fly before a level is loaded and the CPU requires much memory.

Need more texture memory fine just make the AI multi task in the available memory left. It may be a little slow but the 360 CPU whilist not the Cell can more than cover up momentary stalls.

The Key thing to realise is that the 360 memory can be constantly reallocated which makes for one heck of a powerful solution for Developers to toy with.

The memory architecture coupled with a fully specced GPU is the main reason the 360 has been able to slug it out toe to toe with the PS3 so long.

Rest assured however SONY are no fools they will have learnt from their mistakes and I doubt the PS4 will be handicapped in the same way as the PS3.

Oh I should add the 360 memory architecture is probably the biggest fluke in the world.

I am lead to understand that shortly before launch Microsoft feared the PS3 would launch with 512 MB of memory as the original 360 had been planned to only have 256 MB.

In a panic not to be outdone MS shifted to a 512 MB architecture but the only memory commerically available at such short notice was fast 512 MB DDR3. In order to counter anything SONY could manage they went for a unified architecture.

So there you have it, Microsofts stroke of genius was the result of blind paranoia.

I thought the reason the 360 has 512MB instead of 256MB was because of Epic Games. Didn't Cliffy B say the begged MS to up the RAM to 512 when they developing the first Gears of War?