The warning stems from a new check in the wrapper script. I added because some users had problems accessing audio devices without being member of the audio group.
Seems that audio access is fine in F18 for users with default setup (pulseaudio). Perhaps best to just remove this test. You can do it yourself by patching the /usr/bin/spotify script. Otherwise, stay tuned for an update.
If you follow the "Solution" link form the top of this thread you will find instructions how to build your own RPM.
Spotify only distributes a Debian package. While I think this is a bad idea, they are certainly not alone these days. Furthermore, their license terms prohibits re-distribution. That's why there's just instructions to build a rpm instead of a download link (see the sticky thread on LInux license terms). These license terms are an even worse idea, and quite uncommon for a company in Spotify's position. Let's hope they change their mind,
Not that I find it hard to understand your position, not at all. That said, if waiting you'll have to wait until Spotify changes their license terms which probably doesn't happen overnight. It was actually quite recently they clarified those terms.
Also, you don't really have to know how to build a rpm to follow those instructions. Having used a terminal window a little certainly helps, though. In this 9-page thread no one has so far reported any problems building the rpm.