[basjoos]

A clutch is worn out by how much slippage it gets as you engage it. The clutch lining is like brake lining in that a little of it gets scraped off each time you engage it when the engine and transmission are spinning at different rpms. As it speeds up or slows down the engine until it matches the transmission rpm, it is rubbing off clutch lining. If you did mostly highway driving and rev matched each time you changed gears while in motion, the transmission bearings would wear out long before the clutch lining would. If you did mostly city driving in a hilly location, often towed a trailer, and didn't rev match when changing gears, the clutch lining would be the first to go.

I've heard people saying that if you spent a lot of time coasting with the clutch pedal pressed down so the clutch was disengaged, it would wear out the throwout bearing, but I have never had one fail. When Greasemonkee replaced my transmission after 515,000 miles, a 5th gear journal bearing had failed, but it still had 1/3 of the clutch lining left and throwout bearing was fine.