It's rather old news, but today it has been finally set as default—yes the wallpaper for Fedora 18 Spherical Cow release. It took so much time because I didn't manage to update the package that sets the defaults in time before Alpha freeze.
You probably have a general idea of what the wallpaper looks like from my post about pre-alpha version of it, but since then it has been polished a bit—mizmo did a great job on that—and now it looks like this ;-)
Update Sep 08: I'm not the author of the wallpaper, just a packager, so do not thank me ;-) However, I'm relaying your feedback to the design-team, so I really appreciate all the comments you've posted so far. I'll keep both my readers as well as the design team informed about news on both sides, so comment more and stay tuned for updates ;-)