Both ghacks and Google Operating System are talking about a cookie Google/YouTube is experimenting with in order to remove ads, which of course means that you can just write this cookie into your browser and remove ads while it's activated. While there are browser add-ons that allow you to do this anyway, this is an actual official test by YouTube in their continuing efforts to always be experimenting on things. No doubt, it's a test of user experience on the site. The question is, if people like this a lot, what would change?
A Look at the YouTube 'No Ads' Cookie
You can get the full instructions (like how to access your browser's developer console) here on Google Operating System, but here's the basic steps:
1. Open YouTube.
2. Go to your browser's developer console.
3. Enter the following:
document.cookie="VISITOR_INFO1_LIVE=oKckVSqvaGw; path=/; domain=.youtube.com";window.location.reload();
4. Close the console and check it out.
If you want to go back, you can change the code from Step 3 to this:
document.cookie="VISITOR_INFO1_LIVE=; path=/; domain=.youtube.com";window.location.reload();
I have no idea why YouTube, which is viable to many creators through ads, want to figure out how the user experience is without ads, unless they just want to see if people watch a lot of extra videos when they aren't present. Anyway, check it out if you'd like. It probably won't last much longer.