[marcamillion]

They do have real value. All central banks and banking regulators use them to determine the quality of the collateral that can be posted.

So, for instance, say you are a big bank that wants to borrow cash overnight at a low-interest rate - you have to put something up as collateral. Various central banks have various instruments for various things, but for the most part they tend to require 'investment grade' securities - which is why Greece has been causing such a kurfuffle because if they have a 'selective default', then the ratings agencies will downgrade to junk status and financial institutions won't be able to use Greek gov't bonds as collateral anymore.

That's an overly simplified case, but that can be extended to any where that requires collateral. Most, if not all, financial institutions swear by those credit ratings.