Yeah, defragmenting is probably something that doesn't need to be worried about.
But as we know, drives on Macs do go bad. Drive Genius and is one of the few tools available that will work reasonably well with Mac volumes to recover files from a disk that is dying. An older article of some more of them is here: http://www.peachpit....cle.aspx?p=693649 Having an external backup is a good idea, but that's not failure-proof either.
Having a tool that monitors SMART messages from hard drives is probably a good idea, as it can give advance indications that a drive is dying. I haven't looked for one of those yet, myself. http://www.apple.com...smartutility.html is one. There are some messages out there that indicate there may be something free in the POSIX tools that's part of OS X - I haven't looked carefully.
And having a system monitor tool is very handy in some circumstances. E.g. Our old G4 Titanium Powerbook was throwing up the spinning beach ball quite often while browsing, for unknown reasons. iStat Pro made it clear that it was happening because it was running out of RAM and hitting the swap file too heavily. Since it only can take 1 GB of RAM, other than changing browsing habits, it was something that had to be accepted. But without iStat Pro, it wasn't possible to easily know what was going on.
Yeah, futzing around with utilities can be counter-productive, but it's nice to know what exactly is happening and what can be done when things are going wrong.
Ashton - a good resource that you should browse occasionally is Ric Ford's "Macintouch". Lots of user tips, pointers to cheap deals, notes about software updates and issues, etc. It's a great resource.
http://www.macintouch.com
My $0.02. :-)
Cheers,
Scott.