Also annoying is the placement of such devices. They sit directly below the keyboard. Many a time have I accidentally brushed my wrist against it and the pointer moves to some completely random place, and my text goes askew. I've also noted a few times when it was impossible that it received direct input from me. This would point to either it receiving presses from the chassis of the notebook being pressed upon, or it making up its input, in response to some other natural phenomenon.
An interesting design point of most touchpads is the way they handle the actually finger-press. If you accidentally put another finger down (common occurrance, believe me), the pointer will jump. The distance is determined by the midpoint of the line between your fingers.
This fact can be used for a temporary diversion, I've found. You touch with one finger, then place the other down, then lift the first finger. The pointer will "walk" across the screen this way. Not very useful, but when you've been on the phone for 15 minutes listening to silence, anything goes.