I made
a video of the Tango GUI on a Nokia N800 (which has the same resolution touch screen - but is just a tiny bit smaller than the Pandora - 4.1" instead of 4.3") and my PSP Slim (so you could see it on a game system. These are just slideshows of the pictures you've already seen on here. So, it might just be a waste of time. You have been warned.
First of all, I do love your GUI (although I'm enough of a geek to want to try out your text-based "alternative"), so consider the rest of my post as nit-picking:
1. I don't know if this is feasible, but couldn't the bottom tabs be aligned with the number keys of the Pandora's keypad? That way it would be rather easy to assign a <FN>+<NUMBER> combination to each tab. You know, for the touchscreen-impaired.
2. I'm still a big fan of a tile-based layout, mainly because it removes the ambiguity of where the clickable zone for an icon ends, so instead of having loose icons in the grid-based layout, perhaps true tiles (you know, with outlines) could be used. It's probably visually less appealing, but I'm betting it'll score big in the usability area.
3. Please, if possible,
no kinetic scrolling! It really drives me nuts on a small screen (and is the main reason why I don't use Canola on my N800!). Gesture scrolling, especially on the slider layout, might work, but I'd seriously urge you to make it a user-definable setting.
As to the rest: Kudos on taking the good bits of Maemo and leaving out the lousy bits. Just make sure the top-right toolbar is expandable and user-accessible, that the home widgets are resizeable and can be locked in place and that there is an easy way to go in and out of fullscreen mode (i.e. without tabs and widgets).
Actually,
this is a good place to find out what's wrong with Maemo from a usability point of view. Obviously, the Newton-specific points are less important, as the Pandora is not a handwriting-centric pocketable, but there's some very good stuff in there.