OK, this was posted on /. and I was very ho-hum about the whole discussion until found this posting by the author:

[ http://slashdot.org/comments.pl?sid=45250&cid=4688670 ]

Since I'm the creator of PicoGUI, I thought I should elaborate a bit PicoGUI is designed with a lot of goals in mind, but for me the largest goal is scalability. I'd like to be able to run one app, with minimal code changes if any, on a PDA, desktop, cell phone, phone, toaster :)

There are also a lot of architectural decisions PicoGUI makes that lends itself to easy and consistent solutions for common problems other GUIs have to deal with. PicoGUI has a theme system that manages everything from drawing the widgets to laying out entire application UIs, all with surprisingly little code. It has a video driver architecture that handles raw framebuffers, accelerator cards, and even esoteric devices like ncurses rendering or text-mode LCDs. PicoGUI's widgets are designed with more of a UNIX philosophy- small but powerful widgets that can be combined in nifty ways.

I didn't originally intend PicoGUI to be a primary GUI for desktop computers. I started it for a PDA project I was working on. But, given how its architecture lends itself well to scalability, it could soon be a good GUI for desktops. Recently PicoGUI gained the ability to run in a "rootless" mode where it acts more like a widget toolkit than a complete GUI. Once PicoGUI has drivers for DirectFB or some other acceleration backend, and a way to run X apps in an emulation mode, it should be able to completely replace X.

In my opinion, the biggest stumbling block to replacing X on the desktop is having accelerated video drivers that work on other GUIs. I've talked to X developers about separating the video drivers into a layer that can be used directly by projects like PicoGUI, GGI, and Fresco, but they had no interest. From what I've seen of X developers, they want all the world to run in X.

Which I found very interesting. I'm pretty tired of both Windows and X. I'll found out how MacOSX is shortly....