This won’t be big news to a lot of folks, but it’s pretty critical if you spend a lot of time in our analytics data. Google has refactored how the handle visitor sessions and this will have an impact on stats that have to do with time on site, page views per visit, etc.
Historical data will be maintained so you don’t have to worry that they have retroactively adjusted your site stats, but moving forward we can expect to see a shift in how these values are calculated.
Do you use the Google URL Builder?
If so, be careful changing the values for your campaigns, as the new changes can cause a new session to be triggered, significantly monkeying with your session data for visitors. It’s unclear how much effect URL parameters may have on session tracking, but based on my read, it could be significant.
One small side note – there were also some technical issues with the rollout and you may have noticed some very strange data during the rollout. All should be fixed now.