"Oh my god, I can't believe someone who considers him/herself an "expert" almost never defrags a hard drive?!"

For me the reality is that in my situation defragging isn't necessary. My OS lives on it's own partition and is almost completely unfragmented because there is very little data writing happening to that partition. Similarly the drive I store my software on doesn't fragment a whole lot because the installs are fundamentally linear in nature as to their writing.

There are only two partitions that get thrashed in the way that would require defragmenting, and in neither case is there much point to it. The drive I keep my personal data on (Outlook files, My documents and so on) does fragment all to hell... but if I defragged it tonight it would be trashed tomorrow as soon as I started using the drive, it's basically pointless. Similarly, the large partition I use for video editing and animation rendering gets written with huge files that are created and destroyed fairly often... there is rarely a purpose to the defragmentation as again the drive would get trashed in short order. The large files tend to be similarly sized so they rarely micro fragment.

These days drive fragmentation is an issue of read/write performance, and not stability. My XP box is rock solid no matter how fragmented the data it is using gets... if I see an extreme slowdown I might defrag it, but that hasn't happened in more than a year. Thanks to firewire, packet writing DVD drives and a fast drive bus I never drop a frame, burn a coaster or whatever and the render times on my 3D work is generally so long with GI and so on that the time to write a frame isn't a factor.

It's all about partition planning. All but two of my partitions change rarely if ever and are extremely "clean" linear lay downs of the software and data I use. It lets me avoid a lot of the defrag cycle :)