I don't think it would shorten the drive's life all that much. If you are de-fragmenting every day, chances are that the drive will not get that fragmented, so after the initial defragment, the amount of seeks/read/write cycles should be at a minimum.
Though I don't really see why you would want to defragment every day, that seems a bit excessive to me. What are you doing to the drive that is causing it to fragment enough to warrant a defragment every day?
it adds more reads and writes, but can reduce how many it has due to the files being defragged.
it all depends on what defragment method is used - is your defragger ONLY messing with fragmented files, or does it re-order files, move them to the faster parts of the drive, etc.
The more activity your defragger causes, the less often you should run it.
How modern the drive is has nothing to do with how fragmented it is/will get. It is all about how the data is written to the drive.
its all about how the
OS writes data to the drive
Nothing really, I just do it cause it takes no longer than 5-10 minutes to complete. When I used to do it weekly, it would take at least 45-60 minutes and sometimes a bit longer to complete.
5-10 minutes sounds like its only touching fragmented files, and therefore isnt going to stress your drive too much. if its that quick, your performance gains would be zero and nil, however.
Would of thought they'd have had better controllers on the HDD PCB etc.
Newer drives do seem to fragment less at any rate.
My IDE drives needed defragging every month and were approx 30% fragmented.
its got nothing to do with the HDD at all. its all to do with the file system used, and the OS.
Why would you defrag your hard drive every day? Your hard drive doesn't get fragmented unless you put stuff on it. Only defrag after you make a large instillation (like a video game) or move a bunch of files.
Thats my way of thinking as well - i defrag maybe once every 3 months, but i have a logical HDD setup to prevent fragmentation
C: drive for OS only, games and programs on seperate partitions - its only the programs that write constantly that fragment your drive, so keeping my non-changing files (games) on a seperate drive or partition, prevents them ever fragmenting.
I tell you what's strange. I work in IT and when I look at user's computers I see that just using the PC with limited rights and storing everything on a network drive (nothing saved to the local HD) fragments them badly. This goes for both Win2k & XP.
Especially the older Win2K machines will have solid red showing in the defragger and run like treacle. Defragging them improves the response times significantly.
Why it should fragment like this I don't know.
because they're running old OS's, and likely fat32. as you said, the older machines on the older OS are worst, because MS tweaks that stuff as they go along with updates to the file systems, and how the OS writes to the drives.
NCQ has helped, but really the drive has little to do with where data is placed on the drive, the program/OS writing the data to the drive contols where it goes on the drive, and how it is fragmented.
For the most part, modern OSes have gotten better about keeping drive fragmentation to a minimum.
this man beat me to it. one cookie.
Sheesh, are you a moderator or a troll? You're manner is extremely rude and offensive. This is not the first time you've behaved this way towards me, either.
while not aimed at me, i have one thing to say: never pick a fight with a moderator. you lose the moment you try.
Some hardware we rush its death! 
I say if you install and uninstall things a lot you really have no choice but defrag. I Defrag often maybe every other day. I dont think its that harmful really.
I'd be grateful to anyone that does know.
In hindsight, I think saying "troll" was a little too heavy and unfair, whether I had a point, or not, so my apologies to Sneeky for that. I can't say any more though - was discussed in PMs + off topic here. (Things are good now, BTW. 
