I, too, am curious if the "rules" have changed from OS 8-9 to OSX -- concerning "desktop" files, that is.
Under OS 8 and 9, disk fragmentation was an enemy to well-behaved Macs. This could result from files being strewn willy-nilly on and off the "desktop" for a period of time. This discovery lead us to become strong believers in partitioning disk drives. Our B&W G3's at work are partitioned into four spaces -- SYSTEM (about 1Gb just for the System Folder), SCRATCH (1Gb for Photoshop, Illustrator and Virtual memory to use), APPS (2Gb for applications only), and USERFILES (the remainder of the drive where the user is supposed to store their stuff.)
Our preaching this gospel further said that if you absolutely MUST have files on the desktop, first store them in USERFILES and then make an alias to the desktop. That keeps transient file traffic off the SYSTEM partition and significantly decreases fragmentation, which the System Folder does not like.
This has worked well for several years and has reduced our tech support calls measurably. If there is a problem, 10 minutes running Disk First Aid, Disk Warrior and Plus Optimizer on the SYSTEM partition and the user is back in business and the errors have magically disappeared!
Now, back to OSX. Because this is UNIX based, are these "rules" obsolete now? Does the system suffer from disk fragmentation like OS9 did? Thanks.