Getting back to the original post on S&P downgrading Centro. They've lost plenty of credibility given their role in the sub-prime mess which ultimately caused the credit crunch.
Here's a link to an interesting article in the NZ Herald titled "How sub-prime crisis made fools of credit raters" :
http://www.nzherald.co.nz/section/3/story.cfm?c_id=3&objectid=10484973