Yep, but this isn't due to GTK. This is due to Glib & GStreamer. Adding GTK to primitive gstreamer-based app adds only 3mb.

Okay, i'm not insisting on using GTK. After all, such non-generic UI will not use the core part of GTK — standard widgets. Simple pixmaps-based widgets and handling touch events can be implemented as thin abstraction layer over Xlib.
So, okay, i'm going to agree with you about GTK Small & simple X-based UI toolkit seems to be enough. And this toolkit can be reusable in other projects

(By the way, I already have some little experience in writing lightweight UI toolkits: I did one over WinAPI when developed project for Windows CE. Qt & Gtk was too heavy for device with 32mb RAM and I have created my own, because coding with plain WinAPI is even more ugly than with plain Xlib )

And if we are dropping GTK, Vala might be the next, because the main advantage of Vala is the ease of using GTK. And ok, D-Bus can be handled manually too

But using GStreamer will eat 8-10mb of ram anyway. And i don't know how we can do anything about it.

About the UI. I *love* these mockups! The last one with settings menu is really amazing (except checkboxes as auouymous said).
But unfortunately blurred background is not the case for N8x0. We have no OpenGL shaders which can do this easily. And blurring with CPU is really expensive. I think the most we can do is to dim background with plain color.
And yes, close button is not from here. It seems to be from Windows Vista


This seems to be pretty easy to do with gstreamer


Kroll, i think it's time to start working out some formal technical requirements. Could you create some public Google Doc for it, please?