I personally prefer these over trackpads, which I consider evil. In fact, when getting my laptop for college, this seemingly trivial detail was the reason many were dropped from contention. Precision movement is quite possible with a little effort, and I have even successfully fragged using one (makes it really convenient to throw grenades in TFC, too ;).
My only complaint about nipple meeces is that the rubber ones used by Toshiba and Dell (and probably others) eventually lose their texture and become increasingly difficult to control, prompting the replacement of the spent nipple mouse with a fresh one (often with relatively exorbitant prices for replacements (on the order of $2-3 per nipple)). IBM models use hard plastic, which, AFAIK, is not replaceable, but lasts much longer. If they are replaceable, I intend to get an IBM nipple mouse to put on my Dell laptop when its current (rubber) nipple mouse wears out.
generic-man says re nipple mouse: IBM's nipple mice tips are replaceable; some ThinkPads even come with different shapes for you to try.