should I reformat?

[dylanb2cm]

Do Mac's need to be reformated and if so, how often?

[Case]

I consider reformatting a very last resort to computer trouble. Too much trouble to go through unless you absolutely have to.
I did reformat when buying a second-hand G4 some years ago, to start fresh from whatever the previous owner left behind. I also did a fresh system install after buying a bigger boot HD. I wouldn't do it for regular maintenance.

[terryj]

what kind of problems are you having?

As Case pointed out, this should be considerd a drastic last resort.
Other things that are easier to do and fix most of the problems
that you can encounter on a mac can be fixed by running
diagnostic tools such as DiscWarrior and Disc utility,
or by running System maintence tools such as
Onyx or Cocktail or Macaroni.

[live4ever]

The only time I really reformat is when upgrading the OS to a major new release (ie. Jaguar>Panther>Tiger).

Usually problems are User related (preference, caches etc.) - and if the problems persist with a freshly created user account only then a reformat might be in order.

But you are creating daily backups/clones (with SuperDuper! or CCC) to an external Firewire drive daily it'd be easy to revert to a working stable clone if something did get stuffed.