Made a FB mockup awhile ago for another thread. Thought it would be relevant here as well.
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I think Conner Monsees (UI designer for 6tag and 6sec)
Conner Monsees on Behance has a really good grasp on all the variances of the Modern UI style. I really like his Verge and Pinterest concepts.
I think the pivot style works from some apps and allows for easier design porting from iOS and Android. The Modern UI allows for a lot of leniency for a lot of variance in design so I hope not every app starts using the pivot style (it'll get boring quick). As for the older header style, it has become quite an eye-soar in some apps, it makes it kind of messy (dark backgrounds w/ white text more so) *cough *cough ESPN *cough *cough. With all that said I'm really looking forward to see what the final official Instagram app will look like and how it will function.