How to mix the perfect wasabi...

It's often the case in sushi restaurants that the wasabi comes out on the same tray as the sushi.
This is unfortunate because many people bide some of the time between placing the order and the arrival of the sushi by preparing their dipping tray. But you have no wasabi yet, right? So what do you do? You fill it with soy sauce. Resist this urge at all costs. Wasabi floats, as you've no doubt discovered if you do this often, and it's damn near impossible to get those last few wasabi bits properly dissolved and incorporated. Now, if you like surprises, by all means keep doing it this way. If you prefer not to have your jaw fall off and your nose explode at random times during the night, read on.

If you absolutely must do something with your tray at this point add a small amount of soy sauce and roll the dish around to evenly coat the bottom.

The secret to the perfect wasabi fusion is to add the soy sauce to the wasabi.
Get an appropriate amount of wasabi and put it in your dipping tray. What's appropriate for you can be determined by experience. Use as little or as much as you dare.
Poke the wasabi repeatedly with your chopsticks. The main idea here is to break up the surface of the wasabi and not so much to get it flattened to the bottom of your tray. Increase the surface area of your sample, right? Right.
Now add a little soy sauce. Not too much! Mix this in with your wasabi until you've got a nice thick paste.
Add a little more. Mix. Repeat until desired consistency or color is achieved.

20020922182309, Node Tending.

This is in response to mowph's write-up below.
To those that would consider the source, Ryuichi Yoshii has a reported tendency not to offer wasabi on the side when sushi is served in his restaurant... because it already has the perfect amount as determined by the chef. Uh-huh.

I've no clue why mowph mentions sensei's writeup in regards to the "green slurry" question, as there's no deprecation of the method there- merely a warning not to overdo it.

Which, I suppose, is the same warning Yoshii is offering us... though with the assumption we wouldn't know better than to mix too much wasabi in with our shoyu and are best off not doing it at all.