Yesterday Fedora 18 was finally released. Some major changes include NewInstaller (newUI) which is the new Anaconda installer, FedUp (FEDora UPgrader) which is a new technology for upgrading Fedora installs and Secure Boot which I have discussed elsewhere.
Here are pointers to:
Common Bugs has an entire section on the new Anaconda installer and is pretty extensive. You really should read this before attempting to install Fedora 18. New Installer has a general overview of the new installer, a fairly detailed explanation of the storage workflow, notes on several known temporary limitations of newUI in Fedora 18 such as shrink missing from guided partitioning, repo configuration restrictions, etc.