mac runs slow

If your Mac is on 24/7 Mac OS X has it's own maintenance runtimes which happen automatically.

If your Mac isn't on 24/7 there are a number of things you can do, but it's probably easiest to download a program called Onyx from here:

http://www.macupdate.com/app/mac/11582/onyx

If you scroll down to the bottom of the page, there are links for different versions of Onyx depending on your version of OS X.

Once installed, just keep the default settings and run the maintenance routine within Onyx and your system should hopefully get a bit faster.

Hope this helps.

Open Activity Monitor, Show:>All Processes, sort on CPU%, see if anything using too much CPU% when this happens, click on Memory tab, do you have many Pageouts?

Open Console in Utilities & see if there are any clues or repeating messages when this happens.