I recall this being debunked (at least for airline tickets) completely in a stack exchange thread that was posted here a while back. I'll add the links if I can locate them.
While I can not verify concretely whether or not airlines change prices tied to cookies, I know that it's outcome is suboptimal. Changing prices over a hunch that people will perceive the price as going up or down does not actually convert to more revenue.
Most price changes, even if they are minutes apart have to do with supply and/or time changes.
At ventata, we have an API for limit supply pricing strategies and time/supply are the biggest factors.
Edit to add links:
[1] http://travel.stackexchange.com/questions/2952/flight-ticket...
[2] http://blog.getinvisiblehand.com/2011/04/08/ryanair-manipula...