Looked into this and did some research before for a client. Their are a few problems I encountered and therefore abandoned the idea. The main problem is most Hosting companies are notorious spammers. Just look at the WJunction Hosting area. It will be very very difficult for you to tell which is a real review and which is a fake review to increase the rating and gain more customers.
I considered even going to the extreme of getting Hosting Companies to host a tiny verification file that would confirm the person was hosted with them along with gather data like uptime, speed etc. but even this would be easy to tamper with.
In short I concluded it would just become a spam, flaming and advertising mess.
