Shimano Component Group Release Dates

y-o-y - 2010-10-05 8:24 AM Does anyone know roughly when each of the Shimano groupset series were released?

For example (these are made up, of course, otherwise I wouldn't be asking the question):

DA 7900 - 2011 model year bikes
DA 7800 - 2009 model year bikes
DA 7700 - 2008 model year bikes

Ultegra 6700 - 2009 model year bikes
Ultegra 6600 - 2006 model year bikes
...

Any Ideas?  This informaiton would be immensely helpful for a used bike shopper like myself.