What if you wanted to decrease anonymity? My idea is to be able to build "credit" for an individual. Lenders of BTC could just use a service to check the "credit score" of a certain address of a borrower. The borrower would have to spend a year(s) using one address like a checking account, and by meeting certain criteria over time, they'd earn a higher credit rating. But this doesn't limit them to one address, only to one public address.

You'd have to data mine transactions to and from known/published public addresses of public companies or employers/employees, etc. All of this data about an address could be pulled off of the blockchain and calculated with certain weights, which means no reliance on a P2P rating system. An applicant for a loan could even provide their daily use address (like a checking account) and their offline address (like a savings account). Lenders would rely on the ADDRESS's credit rating, not the individuals.

Is it possible? Am I oversimplifying?
Trying to build a centralized credit system would require a mint, which is why this protocol was build in the first place. We don't want mints and on top of that we don't actually need mints for most functions. I would suggest you take a look at those whole new possibilities that come along with this protocol, such as coloring, escrow services, etc and forget all about the old-fashioned and in many cases incapable credit scoring system. Or, if you insist, try to make use of the all-public transaction log after you have associated an entity with a public address, maybe with a micro-payment or the such.