I'm going to have to disagree with jbaz and say that clutchless upshifts do nothing to wear out the clutch. Clutchless downshifts wont wear it down either, but you shouldnt do them, cause you are risking bending your shift forks for no benefit.
In its heart, a clutch is a type of a brake, only instead of engaging contact between a rotating and stationary plate it contacts two rotating ones.
Clutch damage can be seperated into two components. One is plate wear, which is kind of like wearing your brake pads. They series of plates are a wear item, designed to be replaced. What will wear them is temperature and ammount of time they are rubbing against each other (when the clutch is in the friction zone). Drag launches are brutal on the clutch, you can kill one in a day. Clutching wheelies are the next biggest cause of wear, but it isnt nearly as bad, since you arent transferring all the power the engine can make like you do in a launch. Everything else is pretty negligable, unless you are bad at doing burnouts and have to feather the clutch for a long time. Feathering is bad.
The other component of plate wear is temperature. When the clutch gets hotter it works better, but wears faster. If it overheats, it works worse and wears even faster. Most clutches are oil cooled (italian bikes and harleys are the exception), so having proper oil is critical. Having too little oil or having oil thats too far broken down will destroy your clutch along with the rest of your engine. Also, if you have a slipper clutch it will wear faster, since it automatically goes into the friction zone when you downshift, thus wearing a touch more.
The other component of clutch wear is wear on the structural parts of the clutch, mainly the basket. This is damage that isnt supposed to happen, but will if there are sharp impacts. An unevenly wore chain is a big culprit, as well as popping wheelies (power wheelies are worse than clutch ones here). Baskets arent too difficult to replace, but they are likely to be expansive. The danger here is that a basket can fail catostrophically, and send pieces of aluminum into your engine to mess up who knows what.
The third theoretical component is bearing wear (in cars its called the throw out bearing, I have no idea what the term in bikes is, but its where the actuator connects to the rotating clutch). it would be really easy to fix, and I have never seen one fail, ever. How you use the clutch shouldnt have much of an effect on how quickly this part will wear, its just a matter of operating hours. Anyways, dont worry about this.