A little over a month ago, Google announced that it would stop people, after a 30 day period of time, from rotating their AdWords ads. It really upset advertisers to lose that piece of control and advertisers looked for ways around it.
Google actually listened and announced two changes to this update:
(1) You can now opt out of it completely and Google won't stop the ad rotation if you do not specifically ask them to. The opt out form is over here.
(2) They have extended the time of the ad rotation window from 30 days to 90 days as the default. So if you do not opt out, then your ads will rotate for 90 days, giving it more time to collect data and figure out the best model to use.
It makes advertisers and SEMs happy to see Google almost reversing a decision they made.
Forum discussion at WebmasterWorld.