1. Do you have enough RAM (at least 1GB)?
2. Have you run Disk Utility lately and fixed your permissions?
3. If you're having trouble with a web browser, have you cleared your cache/cookies recently? Some people don't do this for years and get hundreds of megs of temp files.
4. Do you have any programs that run in the background or have a component that runs in the background? Have you tried disabling or updating them to see if that helps things?
Maintenance programs are a pretty big waste of money. Especially on a Mac.