A current problem viewing Youtube with Opera 17 is seeing only 360p resolution available for videos that I know are available at higher resolutions. The older Opera 12 shows 1080p while Opera 17 (also Opera 18 referred to as Opera Next) has only 360p available. A check of other common browsers showed that IE and Firefox gave 1080p resolution and Safari gave up to 720p. Since Opera 18 is based on the same engine as Chromium and Google Chrome, it was expected that they would operate the same. Chromium is the same as Opera 17, only showing 360p, while Google Chrome offers the 1080p resolution.

What is going on here? This is because at the current time the new Opera (Opera 15 and on) is not using by default Adobe Flash, but HTML5 for viewing videos in Youtube. Opera 16 is the Android version used on many non-iOS tablets. Chromium probably is the same since it is the open source for Opera 15+. Google (which owns Youtube) still has Flash as the primary Youtube viewer if the browser has the Flash plugin installed. When viewing Youtube with Opera 15+ or Chromium you are viewing a webM file not a mp4 or flv file. So far it seems that Youtube is only releasing 360p resolution videos, even though there are higher resolutions. This is why you see in various download extensions for Youtube videos only 360p and 720p, even though you can only view the 360p resolutions. The understanding is that youtube is converting mp4 files to webM files, the most popular being converted first.

For Opera 17 (the current version) there is an extension that allows overriding the HTML5 and you can use Flash to view Youtube videos. The extension is titled "Youtube Center" and is available in the Opera Add on's. or at the authors site.

For a discussion on Google's changes to Youtube, as of October 26, 2013, see this blog.