Poor contrast (gray on gray) is a big problem, as is tiny text. Not everyone has 20/20 vision -- many people, even with glasses or contacts, don't, because they

Poor contrast (gray on gray) is a big problem, as is tiny text. Not everyone has 20/20 vision -- many people, even with glasses or contacts, don't, because they have uncorrectable vision difficulties -- their doctors will not recommend surgery because the risk/reward isn't worth it, or simply because there is no cure (lots of eye conditions end up diagnosed as 'idiopathic', medical-speak for 'unknown'). Designers with 20/20 vision reading this -- please consider asking around to see if you can find a tester who doesn't have 20/20 vision. Alternatively just check for contrast and maybe view at 75% zoom and see if your design is still readable (Amazon is surprisingly usable at 50%).