for me it was when they stopped doing software sales.
I was super regular here from 2006 (I lurked for a while) until 2010, then I used it casually to check software and such, and would get on pretty heavy from October thru the holidays.
The software data was the sites "killer app". I mean the database is awesome, but without new software data... it well... is also becoming worthless.
End of 2009 Predictions (Set, January 1st 2009)
Wii- 72 million 3rd Year Peak, better slate of releases
360- 37 million Should trend down slightly after 3rd year peak
PS3- 29 million Sales should pick up next year, 3rd year peak and price cut