I have a client with data centres all around the world.  They have a public AS number from pretty much every registry.

Lets consider a smaller part of the picture, just Asia Pacific.  They use maybe 6 data centres in the APNIC area, all using the one public ASN from APNIC.  The data centres do not have a common carrier/connectivity between them.  A couple of sites are connected via VPN, 2 or 3 are connected with one carrier and the others with a different carrier again.  Most sites have more than one link to other sites for redundancy.  All links are either layer 2, or point to point layer 3.  Most sites have 3 or 4 BPG devices in them, all in the same AS.

Creating a full iBGP mesh within a singe data centre is ok.  But I have had to use a lot of route reflectors to build the connectivity between the different data centres.

I have never used a BGP Confederation before, but I am starting to think this will be the most manageable way.  Make each datacentre a a separate sub-AS, because I can easily create a full mesh within a data centre.  Then peering between the sub-AS's will become trivial, while still providing the appearance of a single AS to all the external peers.

Have you use BGP Confederation before?  Had a good/bad experience?