Chrome users who have the AdBlock extension installed are finding that their YouTube experience has been degraded as a result of changes that Google has made to the service.
Pre-roll ads have, in effect, become mandatory. The only part of the video recognized as an advert is the 'Skip Ad' button, ironically, which means that AdBlock users have to watch the whole ad before getting to the content.
Whilst there are easy ways around this, it does hint at what publishers will need to do to defeat ad-blocking, especially as Apple will be integrating it into iOS and, presumably, OS X shortly.
This escalation of the battle between content providers and ad blockers doesn't bode well. However it isn't an unreasonable step for Google to take. Content providers have a right (and if they are corporations a duty) to try to extract some value from the business of providing content.