Apple hasn’t made an official statement. But according to published reports about the developer betas of OS X Mavericks, it appears that any Mac that can run OS X Mountain Lion can be upgraded to the forthcoming OS release. What this means is that if you’re using OS 10.8, you shouldn’t have much to worry about, at least when it comes to your Mac hardware.
If you never upgraded to Mountain Lion, you’ll want to determine whether your Mac is compatible, if not, end of story. There’s no sense reading further, unless a new Mac is on the horizon for you. In that case, it’ll be compatible with Mavericks, and will be preloaded with the new OS within weeks of its release.
In the old days of Mac OS and OS X installations, you had something called a clean install, that basically created a new system setup, but left the older stuff in a separate folder for you to check at your leisure. For better or worse, Apple has given up on that sort of thing. Supposedly it’s not necessary except for extreme situations.