No official numbers were mentioned. But most people estimate the OS and its features to take at most 2GB of it. Leaving 6 for games.

It was a big mistake. The GPU isn't strong enough to take advantage of 8 GB of GDDR5 RAM. Hell, even the most graphically-advanced games use 1.5-2 GB.

Could you please elaborate on what you just said?

I think your right, but why are developers so happy about 8GB, instead of 4?

Lots of VRAM is useful if the GPU you're running the game on is strong enough to render whatever it is you're trying to render. Most of the graphically-intense PC games only use up 1.5-2 GB of VRAM. I understand that approximately 1 GB of PS4's memory will be dedicated to the OS, so that leaves us with 7 GB of GDDR5 RAM specifically for gaming, which is still much more than a 1.84 TFlop GPU can handle. At max, PS4's GPU can probably handle up to 1.5 GB of RAM before it gets pushed to its limit. The question is, where will the other 5.5 GB of RAM go to?

A 4 GB GDDR5 unified RAM architecture with a 2.5-3.0 TFlop GPU would have been a much more powerful console.

I think he means 3.5gb is enough for games, but like you said it depends what they wanted to do with os, it was rumored to be  512mb, when they had 4gb, i think 3.5 is more then enough but then again i'm no developer, i just want most games to take advantage of the extra ram but i'm not really sure, with a more powerful gpu every game will see an advantage.

I'm assuming it's because bad programmers don't have to make concessions with the memory like they would on PS3's 256 MB RAM. They don't have to optimize their code as much, meaning it'll make their developing lives much easier. To the gamers like us, we'll hardly notice the difference.

Devs seem to love it so I'd say it's the right move.

fixed for you, cause some of the best programmers praised the 8 gb of ram in ps4.

I'll try not to jump to conclusions, since I know that a console environment isn't the same as the PC environment, which has a bloated OS that makes it difficult to maximize hardware potential.
I just hope SONY's engineers know what the hell they're doing. After the $599 price-point and the CELL disaster, it's hard for me to have faith in SONY.