Noriko Takiguchi wrote a connoisseur's guide to Sushi back in 2005. It's an example of the highest form of blogging, and I'm linking to it so I don't have to email Dan Gillmor (who is Noriko's partner) to find the URL ever again.
Here's a sample from Part 4 of the series which covers Soy Sauce:
Then comes the more advanced part of dealing soy sauce: How sushi touches the soy sauce before it goes into your mouth. This may be surprising, but you should dip the fish side, not the rice, into the soy sauce. Many people in Japan do not know this, either, but this is critical in good sushi eating. How you do it, however, is a little tricky.¶ 12/29/2006When you pick up a sushi piece using your thumb, first and second fingers, you just turn it over so that the sushi piece is almost upside down. If you are using chopsticks, you might first want to knock down the sushi piece sideways, so that you only need to twist your wrist 90 degrees to dip the sushi upside down into soy sauce..
When you touch the soy sauce with sushi, it has to be quick, almost like a fish jumping up from between the waves. You do not soak sushi in soy sauce. Sushi is after all about freshness and liveliness. So, remember, if your sushi piece resembles yourself in a bathtub on weekends, resting comfortably in liquid very long, you have done it incorrectly.
Many sushi connoisseurs say that it is the fish side, again, that first touches your tongue when eating. This way, you can enjoy the taste and the texture of the fish well with some flavors of soy.
