To simplify the Mark Richt era, there was the 2002-05 heyday in which the Dawgs won two SEC titles and three SEC East titles, and then the 2006-09 decline, in which Georgia didn't win its division even once, despite having very talented rosters. There are two primary explanations for why Georgia came down after 2005:
1. Willie Martinez became the defensive coordinator in 2005, the chinks started to appear in Georgia's armor at the end of that season (specifically, in the Auburn and West Virginia games), and then the defense went into full-on collapse mode at critical points during the next four seasons. If Martinez (and some other position coaches on the defense) was to blame and Todd Grantham is an upgrade, then the problem has been solved.
2. Richt benefited from a weak SEC. Here are the SEC's ranks (according to Sagarin) for the Aughts:
2009 - 1
2008 - 1
2007 - 1
2006 - 1
2005 - 5
2004 - 6
2003 - 2
2002 - 3
2001 - 1
2000 - 4
Richt's heyday corresponds with the conference's weakest period. Steve Spurrier had been replaced by Ron Zook, Phil Fulmer and Lou Holtz were in decline, Arkansas was in between Houston Nutt's two strong periods (the Clint Stoerner teams at the start of his tenure and the McFadden/Jones teams at the end), and Alabama was adrift under Mike Shula. The only SEC power programs that were not suffering were Auburn and LSU and Richt batted .500 against them during the glory years, including the two worst losses of the period: the 2003 SEC Championship Game against LSU and the 2004 game at Auburn. If this explanation is correct, then Mark Richt's future will be determined by whether Georgia's rivals in the conference slide. The conclusion would be that Richt is a pretty good coach who can win when he is in a decent SEC, but he cannot swim with the sharks that have been unleashed in the past four years.
Personally, I see a combination of the two explanations at work. I do think that Georgia will get better with a better defensive staff. I also think that Florida possibly declining under a chilled out Urban Meyer (or, dare we dream, Steve Addazio as the quasi-head coach, a la Mike Debord for 2007 Michigan) and Tennessee continuing to thrash about will be more important in defining the next Richt epoch.