8 generations?? Maybe 5 if you want to count GT300 series, wich is for OEM's:

8800 series
9800 series
200 series
*300 series*
400 series

And from ATi:

HD2000 series
HD3000 series
HD4000 series
HD5000 series
HD6000 series

IMHO ATi is 1 generation ahead, or at least 6 months ahead.