I noticed today that there's a new button in the upper right part of the page, inmediately above the video, to "watch the video in a new window". If you click it, a popup opens with the same video you were watching. In my opinion, it's a cool feature for those who like to browse or do other stuff at the same time they watch a video.
Previously, in the same place, there was another button to "turn the lights off", which aimed to reduce the distraction caused by the rest of the youtube page.
Is this new? Is anybody else seeing it? What do you think?

I saw this before, I think at the beginning of this month.

the button is online since 4-6 weeks on some youtube partner's videos and was added to all videos with last youtube release

http://www.youtube.com/blog?entry=wvt7aEaz38E

I do not get this anymore, I only get "Switch to a bigger video size" where that button used to be. Similar to Veoh.

Its here for me alright... can't see the switch to a bigger video size button anywhere... quess you got caught up in a new experiment???

Pressing the middle button
http://img199.imageshack.us/img199/9184/3wy.png

Makes the video big like this
http://img198.imageshack.us/img198/647/rst.png

James Xuan: Any new cookies by any chance you could share?

the middle button:
eg. here: www.youtube.com/watch?v=jqxENMKaeCU&feature=channel_page