Now before you go off and start flaming me, I just want to start up some discussion. With that said, I believe that Danzou is Tobi; the puppeteer behind Akatsuki. I believe this mostly because:
Danzou has his right eye bandaged up for some reason, and it was just recently revealed that Tobi has the sharingan in his right eye. Perhaps the bandage is just a front to prevent people from seeing his sharingan, or to some other affect.
In addition, Danzou has a disliking for Sarutobi and Shodai's peace-seeking ways, perhaps even disgusted. So it would make sense that the war-loving Danzou would want to create a badass ninja organization hellbent on monopolizing war.
He sent Sai, one of his best, on a mission to terminate sasuke; perhaps it was a test for Sasuke, if he didn't survive he would be deemed "undesirable" for w/e scheme Tobi has for him.
Plus.....their hair is extremely similar
Anyways, this is the only thing i can think of that would make Danzou of importance to the series.