The cycle of trying to find a place to rent is stressful -- either there's a mad rush for people to apply or you're left wondering why the place has been empty for a year. Rent Reviews lets you detail your experiences applying for properties and how you've found places you've rented in the past so other potential tenants can learn from your experience.
Although Rent Reviews lets you rate previous properties, there aren't a lot of reviews from current tenants. This is unsurprising: who wants to piss off their landlord by saying "I live here and the owner sucks"? (While the site allows anonymous reviews, it would be fairly easy for any landlord to work out who had submitted a comment).
The emphasis so far appears to be on describing the rental application process, identifying quirks with particular properties and undesirable potential landlord behaviours. The coverage isn't really broad yet, but it's an interesting idea.