Probably the first article out there where some proper analysis has been undertaken

BarCapCounterparty.pdf (452.09 KB)

and a summary from CreditFlux

http://www.creditflux.com/digest/2008/02/22/barclays+capital+says+cds+counterparty+failure+could+cause+47+billion+of+losses.htm

In summary, BarCap suggest that in the event of a counterparty defaulting, the losses to protection buyers are not as high as the numbers being suggested by others. However, it could be argued that BarCap may be talking up their book!