Some friends now resident in Portland, Oregon, USA brought me a set of "wine glass charms" from JT Designs of Portland in July 2003. So this idea has been realised as a commercial product! Hence I've moved it to my "already done" list.
This is a very simple idea. I would like to be able to buy a set of wine glasses or tumblers that are not quite identical.
This would solve the dinner party problem in which everyone loses track of which glass belongs to whom. Unless your guests get really drunk, they should be able to manage to remember the distinguishing feature that identifies their glass amongst the others. (And if they get beyond that stage, they won't care.)
The trick would be to do this in some pleasing and tasteful manner. Some possibilities would be: