At least one or two people have mentioned this, but (as far as I can tell) always mixed into a post that covers other topics.
Some turns take a really long time. Long engines, engines that requires the player to make decisions along the way (eg, with Hamlet, to discard one card? two cards? for action and/or buy). So, I think A LOT of us multitask as this goes on. We do work on another window. We turn on the TV. We open a good book.
Of course, this means that we don't immediately notice when it is our turn, which is rude to the other player. A small chime would be great. The same--or different--sound when it's Player One's turn but the other player(s) need to do something (discard down to 3 with Milita; select a card to pass for Masq., etc), for the same reason.
Should be really easy to implement, no?