Awesome

Spotifree (DISCONTINUED)

Spotifree is a free OS X app that automatically detects and mutes Spotify audio ads.

Installing

1. Download Spotifree from the website;
2. Move Spotifree.app to the Applications folder, run, and enjoy your ad-free music listening experience :)

On the first run, Spotifree will be added to the login items. From this moment, Spotifree will mute all Spotify ads it detects (usually, all of them). Don't worry though, it will not impact your Mac's performance and you'll never notice it running.

How it works

Spotifree is polling Spotify every .3 seconds to see whether the current track number is 0 (as in all ads). If it is, Spotify is muted for a duration of an ad. When an ad is over, the volume is set to the way it was before.

Alternatives

MuteSpotifyAds by Simon Meusel is a good alternative if Spotifree does not work for you.

Thanks

Thanks Chris Ferrara from MacRumors forums, for the original idea and the proof-of-concept script.
Thanks Eneas, for turning that brittle AppleScript into a robust native application.
Thanks to all other contributors for helping make Spotifree better.