I didn't find either preupgrade or the DVD route to be hassle free. Preupgrade refused to work, finding the wrong boot partition sitting on another disk, unmounted at that. The DVD route put grub on the wrong disk and I wasn't able to make it do otherwise. It also left yum in dependency Heck, as apparently some *.i686 libraries I had installed weren't upgraded and some apps disappeared. Among other things, the kernel wasn't upgraded. By installing/erasing things in bits and pieces I was able to get back to a usable system but it took some work.