Serious question - I’ve only ever upgraded my fedora when forced to i.e. a HD crash. Right now I’m at FC 6 - before used FC 2. Sure I could make /home a separate partition and back all that up but all the tweaks I have to do to things under /etc to get things the way I want them not to mention downloading things like codecs and fonts and getting them all up to snuff?
How to you upgrade an OS so easily and painlessly? It’s always been a major undertaking for me.
I'd recommend a clean upgrade if making a jump that large because there are huge differences between the 2 versions of Fedora. Create a tar of your /etc directory and put it somewhere in /home before backing up. I'd also reccommend an inventory of what you have installed. (rpm -qil > ~/FC6_list.txt) so you can easily reference anything you're missing. Also, if you're upgrading from that far back, I'd have to ask if you have enough ram to successfully run FC12. I'd recommend at least a GB so you can avoid swapping.
Then again, if you're happy with FC6, and it does everything you want it to do, upgrading isn't mandatory, so you're free to stay with what works for you.