I heard a good radio program a few weeks ago on some do's and don'ts for sushi restaurants and I thought I would add a few points of my own.

First off, if it's a "real" sushi restaurant with real sushi chefs, those are trained individuals who take their work seriously. If it's Joe Sushi with regular guys, don't worry about any of this stuff.

Sushi is raw fish. The freshness of said fish can really determine whether you get great food, good food, or food poisoning. Like any restaurant, they will try and move their oldest fish first. IF, however, they respect you, respect your taste, and think you will know the difference, you will get better fish and better service.

-Don't break and rub your chopsticks together. This is saying you don't think the chef/restaurant can afford decent chopsticks. Besides, sushi is supposed to be eaten with your fingers. This allows them to pack the rolls and rice a little looser so it can break apart in your mouth.
-Don't go nuts with wasabi and soy sauce. If the chef sees you hosing down your sushi, he's going to throw the bad fish at you because he may figure you can't taste the difference. (I personally like soy on my rice and I'll dip some when he turns his back.)
-Ask the chef what he recommends! And keep asking. Ask what is freshest. You are then putting him on the spot and he's less likely to bring out his four day old salmon.
-If your chef has a thick accent, don't ask him to repeat what he said 50 times. It can be insulting and embarrassing and is not going to endear you to him.
-Compliment the chef when you like certain dishes.
-You like what you like, but know that the more Americanized sushi (California rolls and their ilk) aren't considered very purist. So if you start with a bunch of that and then grab some fish sushi, you might not get the prime cuts as he may think you won't appreciate it.
-You don't tip the sushi chef, but you can offer to buy them drinks. Just sharing a shot of saki can be good, though many restaurants don't allow their chefs to drink. Still, they will appreciate the offer.
-Learn the correct Japanese pronunciation of the sushi. It's not that hard.

And since I remembered it, some of the better sushi restaurants offer "real" wasabi. The paste they usually give you for free is artificial. The real stuff is a bit runnier, mushier, and vastly more potent. Some restaurants will charge you for it, some won't, but you have to ask. The difference is pretty striking if you like wasabi. You only need maybe 2 pea-sized drops for a full meal. Or at least that's all I need (and all they'll give you). Wasabi is some pretty cool stuff in general. Unlike most hot spices, it is a paste instead of oil-based. That means it washes away, unlike a pepper which just spreads around your mouth if you drink fluids. The real wasabi, I have taken some, and merely swalled saliva and POOF, it's gone. You need to try it at least once.