If you missed Apple’s announcement today here’s the breakdown.
OSX 10.9 Mavericks is a FREE UPGRADE. With great added features and Apps there’s no reason not to update. Download from the Mac App store today. 
Along with the operating system update Apple also announced new versions of Pages, Numbers and Keynote. These versions will be FREE with the purchase of a new machine. However if you are still on iWork ’09 and you want to update you can download for just $19.95.
Apple also update the MacBook Pros with Retinas and the big announcement the iPad Air. We should start seeing new products in stores in early November.