Hmmm.... Lots of comments from people who haven't experienced a good quality short shifter in here I think...
Lets just say that once you've driven around with a good quality short shifter (C's, Mines, NISMO), you will *NEVER* want to drive a car with a standard throw again. It feels sloppy, inaccurate and slow as hell.
Yes, if you rip gears from one to the next as fast as possible all the time and generally give your gearbox a hard time, a short shifter will increase wear on your synchros. Of course it will, your throw is a LOT shorter, and you can crunch the gears if you rip the gearstick with all your strength...
If you drive around like that all the time, you probably deserve to be faced with a gearbox rebuild anyway ... But you can learn to shift as fast as possible without beating the synchros. You will learn how fast you can shift that is optimum for your gearbox, so you don't crunch your gears, and you will then be extracting the very best your gearbox can give you on those 1/4 mile passes...
That's not the best thing about short shift kits anyway. It's for the 95% of the time you're driving on the road and shifting leisurely... It feels so much tighter and direct, it makes the car a pleasure to drive and shifting much nicer...