I recently bought a white unibody MacBook and noticed the same thing -- the sound seemed to come out of the right side of the computer. I opened System Preferences, selected Sound, then messed with the balance settings (because my first reaction was, "wow, it sounds as if only the right speaker is working").
When the balance is set all the way to the right, the sound definitely comes from the right side of the MacBook. When the balance is set all the way to the left, the sound is more towards the center of the computer. The difference is more apparent if you put you face close to the display while changing the speaker balance.
My previous frame of reference is a 2 1/2 year old MacBook -- the model that has two speaker grills on each back edge, about as far away as they can be from one another, so this sounded different.
The speakers in the new MacBook are definitely louder.