I'm a graphic designer and so have always got quite obsessive about the menus in anything I use. I'm always having to explain GUI principles to clients and I must say that I think this is by far the best concept here:
DaveC was on the money, a horizontal bar with more categories and a grid of icons below.
I'd like to see options for the bar being top or bottom (or at the side for people who prefer that) and also any folder on the SD card can become a category. The icon for each category could then be a icon.png file in that folder or a default one if none is present. People can then organise their cards however they like.
I'd also like the system to be fully skinnable for us all to exercise our creative talents on it!
The status info at the bottom is genius, very useful! I think any file manager or music player functions etc should be in dedicated apps, so casually lending the GP2X to a mate is less likely to result in accidentally erased apps or browsing of your music collection and lots of functionality can be packed in where its needed. The launcher itself should be as efficiently streamlined and simple as possible.
Just my opinion, but I'm not a fan of the overload of onscreen info and screenshots etc either, just keep it simple and put things as few moves/clicks away as possible.
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My old GP32 Windups "Themes":
The thing I liked about that was I could place the icons exactly where I liked, line them up or decide what went next to what etc etc, but it was obviously primitive...