Let the server decide. If he or she comes to clear the finished dishes, let them clear them. If they leave them until the last member of the party is finished, don't worry about that, either. I have been in super fancy restaurants where they did it both ways.
The important thing is to be courteous to both the fast and the slow eaters. If someone is still eating their entree, and the server is asking about coffee or dessert, you should all simply say you would like more time. You don't need to be pointed, and say, "We're going to have to wait on that until Pokey-Joe here finishes his dinner," just tell them to check back with you. After the last person has finished the entree, and ONLY then, you can order coffee or desserts, or simply ask for the check, but it should not be done sooner.
And stacking dishes at the side of the table is tacky! Almost everyone I know does it, and it annoys me terribly. If you have to sit and look at the remains of your dinner, be an adult about it, and do it graciously. Don't play with what's left, and don't scrape everything and stack the plates at the edge of the table. Just enjoy the conversation, and leave your utensils sitting neatly on your plate, and leave the plate in front of you until the server comes to clear. It is acceptable, however, to hand your finished plate to the server if he or she has a hard time reaching.