This perhaps has been / is being discussed somewhere else ... if so please delete.

From KLM.com web site for instance:

With SkyPriority, you will enjoy a red-carpet treatment at the airport. [...]
Faster security and passport clearance
Where available, access dedicated lines to help clear you through immigration and security faster.


While this seems to work well in some places, in others (including a favorite hub) it is far from reality. Some even believe the 'dedicated lines' are slower, and often the Airport staff, when asked which is faster, advise to go to the non-priority lines. I do not have hard data.

In some countries (the UK perhaps) false or misleading advertising is prohibited, I believe. Has anyone challenged the Airlines with this SkyPriority Red Carpet thing?

I believe the Airlines should CLOSE the so called priority lines whenever they would become slower (in average over some reasonable period of time, of course).