How often should I...?
 

Defrag my computer, scan for viruses, and scan for spyware and adware?

As often as possible.

Once every 2 weeks or so

reformat every day

I scan for spy/adware like every other day. I try to scan for viruses every 2 weeks at the ver longest. And I defreg like every 2 -4 months, though I should probably do it more frequently.