I *just* took the plunge. This was the cleanest, quickest, dare I say *easiest* Fedora upgrade I've yet experienced (having left it after FC4 and returned at F13). I installed FedUp and off I went. Now running F18. I tried F18-beta on a VM and was pretty unimpressed with the new installer at the time. Time to try it again.
I also noticed the setting for the Alt/Super change under the "Windows" tab in the GNOME Tweak Tool ("Modifier to use for modified window click actions"). So no need to invoke the scary dconf-editor to change it.