I wish Apple added an option for the Notification Center to be displayed by double tapping with two fingers on the Magic Mouse. Unfortunately it's not there.

It's actually VERY easy to do on the Magic Trackpad. Just rest your fingers on the very edge and swipe to the left. You can keep you two fingers touching each other.

I actually ended up doing this by accident a few times when I was trying to go back in Safari. Then I read about the gesture. The difference is that with a regular swipe you don't touch the edge of the trackpad.

Try it. It's easy once you realize you have to have your fingers right on the edge. Let one fingertip half hang off.

I agree with the people saying that this gesture isn't inconvenient. When using the trackpad left-handed, I use David's technique of resting my index finger right on the edge (1/2 off of the trackpad) and the middle finger to its left and slightly up. Right-handed, I find it more convenient to place both my middle and ring fingers on the edge (that is, arranged vertically) when swiping. I haven't had any problems with false positives or negatives, nor with the trackpad sliding to the left.

You can also set a keyboard shortcut for Notification Center in the Mission Control shortcuts section of Keyboard preferences. I chose F5, which is empty on my Apple Wireless Keyboard.