A directory most likely is okay to gather some information about the different companies out there but don't use them to decide who to use. Use forums like this to find out through word of mouth and be sure to talk with the companies directly. See how they treat you and can they answer the questions you have.
I agree - rating a web host based on listings in web host directories would be a mistake. Find the host from the directory and then do thorough research. Always have a backup option that you research, too. Forums are a great way to do research but still - the information you receive needs to be validated. You usually hear more angry voices than good ones. Another good way to find web hosts is via word of mouth from friends, coworkers and family.
directory sites are there to make money just like top host sites. Other than dmoz I don't see many directories out there that simply just list sites. The host directories I have seen always seem advertiser driven. As there is nothing wrong with that, its just the user should be aware of that.