[Sunkist S0D4]

I agree with every with everyone's comments.

Heres something new: I feel like the footers font size is a little too large, the footer kinda blends in with the body. Perhaps make them a little more distinguishable?

[TheyHateUsCuzTheyAintUs]

I don't like the position of the username and password fields, I am not sure why though.

[GenuineGFX]

Looks Ok Only Because It Reminds Me Of An Apple Application Which I Think That If Its For A Site On Global Devices It Shouldnt just Contrast Apple But,
In All Fairness This Is Great I Really Like Every Last Element(Especially The Registration Bar!) . Keep It Up! 9/10

[* Σα]

I agree with cortz and I will also add one thing that is major to me.

A site like Facebook, that is used worldwide by all types of people young and old, needs to be easy to navigate and make total sense.
All of the elements in your design have the same style, plain white.

You need to add more size variation (what cortz said about there not being a hierarchy).
And you also need to fuck with some opacity and make some of your sections differentiate from the others.
All white aint bad but make certain less important things slightly transparent so my eyes know where to look.

[Raz3d]

Nothing really seems eye-catching and the logo is way too small. Something need to take over and lead the viewer and invite the person inside.