[Updated] Try YouTube New Interface

YouTube is testing a new-interface now-a-days. Google is keep trying to improve their service more and more so they will look more attractive and more handy to use.
But YouTube doesn't allow normal users to view its Future Look, here is a little trick using that you can switch to new YouTube Interface.

Follow these steps to get this new style:

Step 1. Go to YouTube.com (obviously :P)

Step 2. Start Developer Console in your Web-Browser Windows 

Google Chrome - CTRL+Shift+J

Mozilla Firefox - CTRL+Shift+K

Opera - CTRL+Shift+I, then select Console

Internet Explorer - F12, then select Console Tab

Step 3. Paste following code here - 

document.cookie="VISITOR_INFO1_LIVE=jZNC3DCddAk; path=/; domain=.youtube.com";window.location.reload();

Step 4. Press Enter and its done,  you can close console now.

[Update] New Layout to Old Layout -

Step 1. Start Developer Console in your Web-Browser Windows (same as previous step 2)

Step 2. Paste following code there -

document.cookie="VISITOR_INFO1_LIVE=; path=/; domain=.youtube.com";window.location.reload(); 

Or to get back your old layout you can just delete cookies for easy and fast method.

The code you pasted actually generate a cookie which force YouTube.com to load in its new (testing) Interface. And its just for a new taste, I'll prefer to use normal look, as firstly its not so cool like present, and it not an Alpha Version, it could have bugs.