Norton's software has been steadily eroding in its popularity because other software that functions better has been around:
Anti-Virus - already covered in this thread.
Firewall - Apple menu -> System Preferences -> Sharing has one built-in, and router and WiFi Access point hardware have even better firewall options that software can't do.
Speed Disk - Mac OS X has done its own defragmentation for small files (20 MB or less). For larger files, having a scratch partition that can be reformatted as needed functions better with less data loss risk. Although partitioning itself will need erasing the hard disk in most instances.
Disk Doctor - Alsoft Disk Warrior and Micromat Techtools Pro offer better directory optimization, and Apple's Disk Utility is less risky for smaller jobs.
Retrospect - frequently this software has needed updating for matching the operating system. Shirt Pocket Superduper, Apple's Time Machine, and Bombich Carbon Copy Cloner have been less sensitive to operating system changes.
Unerase - Prosoft Data Rescue, Subrosasoft Filesalvage, Boomerang's Boomerang, and Stellar's Data Recovery software all recover data without needing to be installed first at varying levels of reliability. A backup plan is recommended regardless, but Unerase will usually need to have been installed first before it can find files to recover.