My trackpad isn't even. It is slightly higher on the left side, and slightly lower on the right side. However, the pressure required to "click" it is the same.
note: My previous unibody MBP (I exchanged mine for a completely unrelated reason) had a trackpad that was totally even. If you're going to get a MBP just because of the trackpad, don't. But that doesn't mean that every unibody laptop has a bad trackpad. It's just the nature of the trackpad since the whole thing is a button. In the previous (non unibody) trackpad, the whole trackpad wasn't a button. This allowed apple to secure it better. When they made the whole thing a button, they need to put in some "wiggle room" for the button.