Maybe you read a lot about fragmentation of files.

If you are an longtime Mac-User, in the past at OS 7-9 days, with old and slow harddiscs, fragmentation was an awful thing.

Since HFS+ and Mac OS X Panther, the file fragmentation isn´t the big problem anymore - if you have much freespace (>= 20 % free).

OS X 10.3+ try to avoid fragment an file at creation time and also tries to defrag files below 20 MB size.

So far , so good.

My GUI-Tool ShowVolumeFragmentation, which uses the hfsdebug commandline tool from Mr. Amit Singh, shows/prints out your file and freespace fragmentation state of any volume.

hfsdebug information from Amit Singh:
http://www.kernelthread.com/software/hfsdebug/