[detaro]

Size probably doesn't matter that much until you start to fill entire datacenters, OSPF nowadays should work with hundreds of routers as well. Would be interesting to see how failure cases compare, if I remember right one of the arguments for BGP in data-center fabrics was that the updates following them stay more localized. (EDIT: a description how Microsoft uses it for really large networks, slide 11 talks about surges: http://www.janog.gr.jp/meeting/janog33/doc/janog33-bgp-nkpos...)

I find BGP easier to understand, and I don't see what benefit OSPF would have. (Not that I really have non-trivial experience with either, have only used them at home and toy networks)