Football Outsiders has complied their "Aggressiveness Index" for 2011 which ranks coaches according to how often they go for it on fourth down. If you've followed people who do any football analysis, they all say coaches should go for it on 4th down more often than they do. FO has a lot more on that if you're interested...
This year, they found that Andy Reid was pretty aggressive on fourth downs, much more so than he has been in the past. He went for it in 9 of 46 opportunities and they were converted just shy of 20% of the time. He ranked at #12 in the index.
However, when they ranked the the least aggressive coaches from 1992-2011, Reid came in dead last amongst those with a minimum of 100 opportunities. The aggressiveness seemed to pay off for Reid this year as the team converted 4th downs at a rate nearly twice that of the rest of his career.
It should be noted that this is definitely a shift in the way Reid acted this season. Their index excludes situations where the team faced a fourth down in opponents territory or was playing catchup late in a game. So it's not by chance that they were going for it on 4th down more often than usual under Reid.
Mel Tucker, who took over the Jags after Jack Del Rio was fired, was the most aggressive coach according to FO. Interestingly enough, it seems that former Andy Reid's former disciples have learned from his caution in different ways. Steve Spagnuolo was the second most aggressive fourth down caller in the NFL, whereas guys like John Harbuagh, Pat Shurmur, Leslie Frazier & Ron Rivera were all ranked in the bottom 20.
Perhaps most surprising of all though is that the most aggressive coach as far as fourth down calls go from 1992-2011 was none other than Rich Kotite.