On Windows, there is Disk Defragmentor that runs every so often to make files contiguous again.
I explain this to users in lay-men terms, but at the same time, I would like to mention yet another +1 about our company, but really have no understanding of the Solaris process to even know if that would work, so how is it done in Solaris?
If it is different depending on filesystem, I it would be nice to know about ZFS, UFS, and whatever the most popular Linux filesystem is.