Google has built a reputation system. It "allows buyers to rate sellers and leave comments." Basically, it's eBay's feedback system. But as John Battelle points out, "Google is not one to get involved in the messy biz of human relationships." And Google isn't just a retail system, a la eBay. Google has an entire host of other services where users could potentially rate providers. ...
I'm not so interested in Google or disembodied reputation systems, but I have to mention something I discovered on my home machine. Quicken - yes, the personal money manger software - now embeds a rating system into the checkbook register, allowing me to rate any vendor or service provider that I enter in my register. This rating is a link to Zipingo.
Reputation systems are all over the place. Amazon, of course and many other eCommerce websites offer mechanisms for rating products they sell. Then you have Epinions that lets individuals rate products they've purchased and links to any online vendors (and ratings of those vendors). Reputation has blossomed far beyond buying and selling stuff, including news services and weblog aggregators. They are all based on the heavily-networked nature of the users of the systems. I cannot possibly rate everything, but I can rate the things I care about or those things which I believe might provide value to someone. And I have to believe in the value that ratings provide to the general populace - that your ratings will help me in the future.
Rating systems have so shown up in places where I am the only one who will ever consume the rating. BlogBridge lets me assign 0-5 stars to each feed with the intention that I can then operate on feeds with different star levels. This is one of those things I just don't get (yet). My "rating" behavior with respect to feeds is generally whether I want to read them at all and how frequently. I deal with that by categorizing (placing them into folders) and changing the order of the feed appearance in that folder.