One of the options frequently mentioned to solve the Euro problem is to issue Eurobonds, because then the bonds will attract the high credit ratings of the core countries.
Only the exact opposite seems to be true according to this from Standard and Poors:
"A joint bond issue by euro zone countries would get the weakest member's rating if the issue was jointly guaranteed, the head of Standard & Poor's European sovereign ratings said on Saturday.
Moritz Kraemer said his understanding was that joint euro bonds would be structured along the lines of Germany's jumbo bonds, in which federal states team up to issue debt and each guarantees its own bit.
"If the euro bond is structured like this and we have public criteria out there then the answer is very simple. If we have a euro bond where Germany guarantees 27 percent, France 20 and Greece 2 percent then the rating of the euro bond would be CC, which which is the rating of Greece," he said. (my emphasis.) "If it is a joint and not a several guarantee then it would be the weakest-link approach, as we call it," he added."
Which leaves me genuinely mystified as to how this is supposed to work? A sort of "portfolio of crappiness, assuming you are yoked together" approach might seem hard to quantify satisfactorily...