Add another to the "Just forget about it" tally. Defragmenting is vastly overblown in terms of importance. The gains in performance can really only be measured with the aid of a benchmarking program, it only improves disk intensive tasks, and the amount of time spent defragmenting a drive will far and away exceed that which is "saved".

Now, if you are running a large web or database server, or do a lot of large scale video editing, then defragmenting may still hold some value. For virtually everyone else, it's a tool that has long since outlived its usefulness. Even in terms of gaming, once a particular map is loaded into memory, the HDD ceases to really be important. Sure you might spend an extra 2-3 seconds over the course of a week, waiting for a map to load on some game, but it won't have any real impact on in-game performance. If it does, it means you are light on RAM and the OS is having to hit the drive for swap space, not that your HDD is too badly fragmented.

Just my opinion anyway. I'm sure there will be plenty of people who disagree, and if someone can actually post some hard data showing that performance improvements are greater than 5% in a broad general sense, not just specific operations, I'd be happy to retract my opinion. I'd honestly be surprised if it's even 1-2% however. I think sometimes people get so caught up in performance tuning that they forget to actually enjoy the fruits of their labors.