Google Analytics Changes Average Time on Site Calculation

Anybody notice something strange with Google Analytics estimates for average time on site recently. We have seen them increase significantly at the back end of July. At a lost to explain this I was glad to come across Brandt Dainow's post on this very subject. It appears that Google Analytics have recently changed the way it calculates average time on site. According to Google Analytics tech support:

"Previously, the Average Time on Site had been calculated as the total time on site for all visits divided by the total number of visits. Both the total time on site and total number of visits included bounces.

As of July 20, 2007, we began reporting the Average Time on Site as the total time on site for all visits (excluding bounces) divided by the total number of visits (excluding bounces). This change also affected data from earlier dates, not just newer data.

I think this makes a lot of sense particularly if your site has a high bounce rate which would make average session times meaningless - but it would have been nice to have been told.