Is there a way to swipe down instead of up to launch Mission Control? To me it feels more natural to "pull" down the Desktop down to access Mission Control however System Preferences for the Magic Trackpad only allow for swiping up to access Mission Control.

Is there a hidden terminal preference or app that would enable swipe down to activate Mission Control?
BetterTouchTool lets you assign arbitrary tap/swipe/click gestures to arbitrary commands.

It supports Lion.