short shifters really don't ruin a transmission directly, however in some cases they may contribute to the wearing of synchro's prematurely. remember, the angle of the shift rod on the shift linkage is not changed when a short shifter is installed...its just lowered making the distance the knob has to travel shorter...and ultimately faster. however, the difference in the time it takes to shift from one gear to the next with a short shifter compared to a regular shifter is not going to affect 1/4 mile times. or if it does...by .001 thousands of a second.

what wears synchro's is shifting hard and without properly using the clutch. thus, if someone shifts hard and extremely fast and doesn't have good timing with the clutch then the synchro's will wear faster.

personally, i don't think short shifters are really worth the money. the 70-100 dollars or whatever people pay for them could be better spent on a performance part that will actually improve performance.