I just finished building the A5 and have begun several firmware mods. (Don't worry, I have lots of experience doing this, check out the current firmware for the Akafugu clock).
One thing that bugged me right at the start though, is the position of the + and - buttons. Am I the only one bothered by this? When navigating the menu, the left button selects the previous item, the right button selects the next, but the +/- setting buttons are the reverse. Drove me nuts until I flipped them in the software. Pretty much every piece of electronics I've ever worked with is left for down or - and right for up or +.
Now I guess I get to make a new top panel for my clock... :-)