Warne is my favorite player, and I do think that Warne's got an excellent cricketing brain, but I think there are some reasonable reservations we might have with him as an international captain, even if the Ian Chappell cheer squad has been pretty unrelenting ever since Steve Waugh got the job. For the record, I think Waugh was the ideal person for the job (and I think his legacy has been extremely unfairly treated since his retirement), and I wouldn't have promoted Warne ahead of him.
I don't agree with the prudish scrutiny that Warne is constantly under, but given the reality that a) he can't seem to stop bringing it upon himself and b)he doesn't like that kind of scrutiny and does his best to avoid the press (to the extent of running to another country) when it hits the fan, he's hardly the best person for a role that requires frequent press contact and expectations for comment like captaincy does. When you are interviewed and you are the endorsed public representative of the team as such, nobody wants your press engagements to become about you more than about the team. It's just the kind of distraction that neither Warne nor Cricket Australia particularly want.
Secondly, I'm not so sure about the "leader of men" part. IMO, Warne can be very hard on those that don't meet his lofty standards at times, but beyond this, I think that some of his actions have annoyed members of the team. In the wake of his diuretics incident, it was palpable that Gilchrist and Ponting in particular were fairly angered by his conduct, and his chequered history probably played it's part in their exasperation.
I probably rate Vaughan, Inzy and Fleming above Ponting (I'd had Ponting and Fleming pretty close previously, but Punter's done himself few favors this tour). If he were to be replaced, I'm not sure who'd get the job, although Clarke is obviously being groomed for the long term. I'm a little surprised at some of the effusive praise for Gilly in this thread, 'cause I don't think he's that special, and I don't think he particularly wants the job either, given the huge job he has in general without the burden of the captaincy.