I've seen a lot of people on various forums recently claiming that defragging reduces hard drive life. I really wonder where this silly idea originated
Defragging is just like any other drive activity..playing a I/O heavy game or watching a divx file - why should it affect the drive adversely?!
If someone is so concerned about drive failure due to defragging, then that person has bigger problems with the overall reliability of the drive itself.
Some people see significant gains after defragging, some don't. It all depends on your usage patterns I feel. I can personally vouch that I do see noticeable improvements in performance after defragging regularly, especially when dealing with large files.
PS:
glc, after your comment in another thread, I tried the Diskeeper set-it-and forget it mode on my drive 1 (media files, P2P and random stuff) which sees heavy activity regularly. Works great. I did run a manual defrag on it before I enabled the auto mode, and it stays defragged quite nicely.