OS X erase & install is easy and effective (I was surprised). But for a serious erase, Apple install disk also offers the deeper 7 pass erase from the disk utility. It takes hours. I've read that this is the level of data shred used by institutions (hospitals, military etc.) With these tools at our disposal, I don't really see the need for 3rd party data shredding software (even though there is some really great freeware out there ;})