Michael Larabel, the principal author of Phoronix.com, has written about his positive experiences with Fedora 21.
Meanwhile, Fedora 21 has been running omen.com with updates since September 14 with good stability.
Yep. I installed F21 branched even before the alpha was released on my desktop at work to check out the support for my video card (which limps in f20 with the random rawhide bits from rpmfusion I needed), and it works fine as near as I can tell. No problems that I've noticed when testing it and the video card works well (though still only with nvidia binaries unfortunately).