ligo,
I think the "Mini-B plug" is not a very good type. Replace it into "B-type plug"
I second that. ta497636 is more polite than I can be. "Mini-B" is bad. There seems to be enough room for a B plug. But I guess that would require a new mold for the case, which is unlikely at such a late stage.
Some more nitpicking:
The menu key is not as useful as a second windows key on the right. Even the latest two keyboards from Microsoft don't have the menu key. A menu key is also not immediately useful under Mac OS X. Perhaps you can make Fn+Right Windows the menu key. That way it is still easy to get to.
The PCB layout also rules out the possibility of a full hhkb layout clone, which doesn't sacrifice the ~` key. If you are going to stick to a strictly ANSI layout, you can make the board even smaller by cutting 1/2 key width on the right, so backspace will be 1.5 key width and \ will be a normal 1 key width. (The Apple keyboard does this.)
Since I'm used to the ANSI layout and the HHKB layout, I prefer to not have to use Fn or a layer key to access ~`. Even though it doesn't get used everyday, it is a very useful key for people typing LaTeX or SQL. (I can't have it all, I know.)
Keep the info coming, Ligo. This keyboard looks very promising.