Regional AS model

I have seen age old discussions on single AS vs multiple AS for backbone and datacenter design. I am particularly interested in operational challenges for running AS per region e.g. one AS for US, one EU etc or I have heard folks do one AS per DC. I particularly don't see any advantage in doing one AS per region or datacenter since most of the reasons I hear is to reduce the iBGP mesh. I generally prefer one AS and making use of confederation. Zaid