This Chrome extension automatically mutes YouTube ads or skips them if possible. When the video starts it will unmute again. You also don't have to wait the 5 seconds to skip the ad, the extension will skip it as soon as it shows up. Since a lot of ads are very shrill and annoying I found this very helpful if you don't want to get some ad involuntarily stuck in your head.
This Extension is now published to the Chrome Webstore. The following Link will get you to the download page.
The Extension will only run on youtube.com* urls. Have fun :)