scroll wheel on mouse should go farther per scroll. It hardly goes anywhere as it is.
(+) and (-) options on quantity box. Or up and down arrows, something to make it so you don't have to use the keyboard in order to increase the qty. Obviously if someone needs 150 or something it will be easier to type it in, but most of the time it is less than 10 probably.
css framework/typography page. Some sort of demo page of what works and what doesn't as far as using html in a splash page. I have worked on this to an extent.
google fonts in templates. Allowing users to use their own fonts is great (designer) but it is not possible to create a nice layout and use pretty fonts as we have no idea what fonts the user has. Google fonts has some nice fonts, if they were allowed then it would be a great improvement. As it is creating cool designs with attractive text nodes is kind of pointless as you have to use safe fonts or else the preview is wrong.
review mode like what events has, only as an option for any order - not just events. That way if someone orders 100s of 4x6 or 8x10s and the files are not proportional you could crop them quickly.