Well, any reading, writing, even having your computer on will enivitably wear your hard drive. But for the most part, in short term, it's barely noticeable. Formating, there are things like Quick Format option in Windows Setup (xp), where it just edit the allocation tables on your hard drive. Your data is still there, it's just not register, therefore it's treated as good as gone. The other format is Full Format which will bombard a sector with a whole bunch crap to guarantee your data is almost permanantly erased. (It normally takes about 7 or so write cycles to almost permantly make 7-write-cycled data unrecoverable, basicaly Full Format will bombard a sector of your hard drive 7 or so times with random data so that things are almost permanantly erased). The latter, I would think, would wear your hard drive more. Again, short term, barely noticeable. Do it daily, probably within a year or less you'll notice your HD a bit more noisy.