Search under my name and "defrag" in the past two weeks. Bottom line of long post: you don't need to defrag your "video drive" under most normal circumstances, and unless you are installing and uninstalling programs on a regular basis, you probably don't need to defrag your C: drive very often either.

Also, defrag is an operation that should be performed only after closing ALL programs, and then don't touch your computer. With most defrag programs, if the defrag detects access to the disk from another program, it will restart from the beginning (at least that is how the older Windows versions behaved).

I disagree. Working with systems that are defragged nightly and systems that are never auto-defragged, all being similar systems, the defragged systems operate much more quickly, more efficiently, and have fewer hangups. Video drives don't need defragging today like they used to because of better management, but boot drives, particularly on machines that spend a lot of time on the web, need regular defragging. You'll see a large difference in performance.
I still hold firm on my practice of defragging a videodrive before capture and after removing a project, or before doing a long print to tape. But as John mentions, it's not as critical now as it was 2 years ago.