because i have a partitioned hard drive on my Mac (i prefer this for working with multimeida projects), the de-fragmenting the 'project' drive is always an issue, and more recently, the need to resize the partitions (since OS X is fussy about what is on the boot drive/partition. having given up on Norton, i have been pleased to discover iPartition and iDefrag fromCoriolis Systems. I've bought iPartition which comes with iDefrag Lite. I'm able to make a boot disk which will allow me to re-partition the hard drive without wiping any data, and defrag the boot drive as well. of course, the application will defrag the second partition and external drive without the need for a boot disk.
it's been excellent value and i highly recommend it.